These Grasshopper Brownie Bars are a layered, no-nonsense dessert that pairs dense, fudgy brownies with a bright mint filling and a glossy chocolate glaze. The recipe uses straightforward techniques—melting chocolate over a double boiler, making a cooked buttercream, chilling, and glazing—so the results are reliably clean, sharp layers when you follow the steps.

I test this combination because the contrast matters: underbaked brownie for chew, mint buttercream for lift, and a thin shiny glaze to finish. Timing and temperature are the quiet stars here. Bring eggs to room temperature and let the brownie cool fully before spreading the filling to avoid a melty mess.

This post gives you the exact ingredient list, method, practical swaps within the recipe, the gear you’ll actually need, frequent mistakes and how to avoid them, and make-ahead advice so these bars show up ready to impress.

What You’ll Need

Ingredients

3/4 cups flour — provides structure; measure by spooning into the cup and leveling for accuracy.
1/2 teaspoon salt — balances sweetness and enhances chocolate flavor.
1 tablespoon dark unsweetened cocoa powder (like Valrhona) — deepens chocolate flavor and tightens crumb.
5 ounces good quality dark chocolate (60 to 72%), coarsely chopped — the base chocolate for the brownie; quality matters for flavor.
1/2 cup (1 stick) butter, cut into 1 inch cubes — melted with the chocolate to create a glossy, fudgy batter.
3/4 cups sugar — primary sweetness in the brownie layer.
1/4 cup firmly packed light brown sugar — adds moisture and a slight caramel note.
3 large eggs, at room temperature — give structure and richness; room temperature helps them incorporate smoothly.
1 teaspoons vanilla extract — rounds and lifts the chocolate flavors.
3/4 cups sugar — used again in the creme de menthe buttercream; cooks into the custard base.
2 tablespoons flour — thickens the milk mixture for the buttercream base.
3/4 cup milk — liquid for the buttercream custard; whole milk gives better texture.
2 tablespoons heavy cream — adds richness to the buttercream custard.
1 1/2 sticks (3/4 cup) butter, softened but still cool, cut into small cubes — whipped into the cooled custard to make the buttercream light and stable.
3 tablespoons creme de menthe — primary mint flavor in the filling.
1 teaspoon peppermint extract — boosts the mint profile; use the exact amount for balance.
6 ounces good-quality dark chocolate (60 to 72%), coarsely chopped — for the final glaze; matching percentages keeps the flavor cohesive.
1 teaspoon light corn syrup — gives the glaze a glossy finish and a smooth pour.
1/2 cup (1 stick) unsalted butter, softened, cut into cubes — combined with the glaze chocolate for sheen and mouthfeel.

Method: Grasshopper Brownie Bars

Preheat the oven to 325°F. Butter the sides and bottom of a 9-by-13-inch glass or light-colored metal pan. Line the bottom with a sheet of parchment paper and butter the parchment.
In a medium bowl, whisk together 3/4 cups flour, 1/2 teaspoon salt, and 1 tablespoon dark unsweetened cocoa powder; set aside.
Set up a large double boiler (large heatproof bowl set over, but not touching, simmering water). Add 5 ounces coarsely chopped dark chocolate and 1/2 cup (1 stick) butter (cut into 1-inch cubes) to the bowl. Stir occasionally until the chocolate and butter are completely melted and smooth.
Turn off the heat under the double boiler but keep the bowl over the water. Add 3/4 cups sugar and 1/4 cup firmly packed light brown sugar to the melted chocolate mixture and whisk until fully combined. Remove the bowl from the pan and let the mixture cool to room temperature.
Add 3 large eggs (at room temperature) to the cooled chocolate mixture and whisk until just combined. Add 1 teaspoons vanilla extract and stir until combined. Do not overbeat.
Sprinkle the reserved flour/cocoa/salt mixture over the chocolate mixture. Using a spatula, fold the dry ingredients into the wet until only a trace of dry streaks remain.
Pour the batter into the prepared pan, smooth the top with an offset spatula, and bake for 12 to 15 minutes, rotating the pan halfway through baking. The brownies should be just underdone: a toothpick inserted at an angle should come out with a few loose crumbs. Remove from the oven and let the brownie layer cool completely in the pan.
To make the creme de menthe buttercream, in a medium heavy-bottomed saucepan whisk together 3/4 cups sugar and 2 tablespoons flour. Add 3/4 cup milk and 2 tablespoons heavy cream.
Cook the milk mixture over medium heat, whisking occasionally, until it comes to a boil and thickens, about 5 to 7 minutes. Remove from heat.
Transfer the hot mixture to the bowl of an electric mixer fitted with the paddle attachment. Beat on high speed until the mixture cools to room temperature (cooling fully is important so the butter does not melt).
Reduce the mixer speed to low and add 1 1/2 sticks (3/4 cup) butter, softened but still cool and cut into small cubes. Mix until the butter is thoroughly incorporated. Increase the speed to medium-high and beat until the filling is light and fluffy.
Add 3 tablespoons creme de menthe and 1 teaspoon peppermint extract and mix until evenly combined. If the filling is too soft, chill briefly in the refrigerator and then re-whip. If it is too firm, place the bowl over a pot of simmering water to warm slightly and then re-mix.
Spread the creme de menthe filling evenly over the completely cooled brownie layer. Place the pan in the refrigerator for a minimum of 45 minutes.
To make the chocolate glaze, set a large non-reactive metal bowl over a saucepan of simmering water. Combine 6 ounces coarsely chopped dark chocolate, 1 teaspoon light corn syrup, and 1/2 cup (1 stick) unsalted butter (softened and cut into cubes) in the bowl. Stir until the mixture is completely smooth.
Remove the bowl from the heat and stir vigorously for 1 minute to release excess heat. Pour the glaze over the chilled creme de menthe layer and use an offset spatula to spread it into an even layer.
Return the pan to the refrigerator and chill for about 1 hour, or until the glaze has hardened.
Remove the pan from the refrigerator and let it sit about 15 minutes to allow the glaze to soften slightly. Use a warm knife (dip in hot water, wipe dry) to cut the bars into squares. Store the bars tightly covered in the refrigerator for up to 4 days.

Why This Grasshopper Brownie Bars Stands Out

Layering a slightly underbaked brownie with a cooked buttercream keeps textures distinct: the brownie stays dense and chewy while the filling remains pillowy. The cooked milk-and-flour custard base gives the buttercream a lifted, stable texture you won’t get from straight creaming; it holds up under the glaze and chills without weeping.

The flavor balance is deliberate. Dark chocolate in both the brownie and the glaze keeps the bars from tasting cloyingly sweet when paired with the mint-forward filling. The glaze’s corn syrup gives shine and a smooth snap when sliced cleanly.

Swap Guide

If you prefer a slightly sweeter chocolate hit, choose dark chocolate closer to 60% rather than 72%; both percentages are listed in the ingredients and work here.
If the creme de menthe intensity is too strong, reduce the creme de menthe by up to 1 tablespoon and keep the 1 teaspoon peppermint extract; the total mint will drop but the profile remains.
If whole milk isn’t on hand, use the milk specified in the recipe; the listed quantities (3/4 cup milk and 2 tablespoons heavy cream) give the right fat ratio for the custard—follow those amounts to keep texture.
Stick to the specified unsalted butter amounts for the glaze and brownie—measured butter impacts texture and the shine of the glaze.

What’s in the Gear List

9-by-13-inch glass or light-colored metal pan — for even baking and easy slicing.
Parchment paper — ensures easy removal and neat edges.
Large heatproof bowl + saucepan for double boiler — for gentle chocolate melting.
Offset spatula — for smoothing batter and glaze into even layers.
Electric mixer with paddle attachment — necessary for whipping the cooked custard into buttercream.
Non-reactive metal bowl over simmering water — used for melting glaze ingredients smoothly.
Knife and hot water for warming — for clean, glossy cuts through the chilled glaze.

Frequent Missteps to Avoid

There are a few common slips that change the outcome. Watch for these.

Spreading filling on a warm brownie. Always cool the brownie layer completely; warm brownies will melt the buttercream and ruin the layers.
Not cooling the cooked milk mixture fully before adding butter. If the custard is warm, the butter will melt and the filling will be greasy rather than whipped and light.
Overbaking the brownies. The recipe calls for a 12–15 minute bake so the center remains just underdone. Overbaking yields a cakier, drier base that loses the fudgy contrast.
Rushing the glaze. Pour the glaze only after the filling has chilled for the minimum 45 minutes and chill again until set. Cutting too soon will smear the glaze.

Holiday-Friendly Variations

These bars lean festive already. A few temperament-conscious adjustments make them holiday-ready while keeping to the recipe framework:

For a more pronounced mint, slightly increase the creme de menthe toward the upper end of what the recipe allows (maintain balance with the peppermint extract).
Serve chilled for a denser, cooler bite in warm settings, or let sit 15 minutes at room temperature for a silkier mouthfeel when serving at room-temp gatherings.
Make the bars the day before a holiday: they hold shape, slice cleanly, and travel well when refrigerated and tightly covered.

Cook’s Commentary

I rely on the cooked custard method for the filling because it’s forgiving: even if the initial pour is slightly loose, chilling and rewhipping will stabilize it. Be attentive when whisking the milk mixture so it thickens properly in the 5–7 minute window; that’s the step that controls body.

Use good-quality dark chocolate in both the brownie and the glaze. The flavor of high-quality chocolate shows through—even after baking and chilling. When I make these, I keep the glaze thin and even so it doesn’t overpower the mint layer underneath.

Make-Ahead & Storage

These bars are excellent for make-ahead. After completing step 16, chill until the glaze is hard, then keep the pan tightly covered in the refrigerator. The recipe specifies storing the bars tightly covered in the refrigerator for up to 4 days.

If you need to freeze for longer storage, cut the bars, freeze them in a single layer on a baking sheet until firm, then wrap pieces individually and store in an airtight container for up to 3 months. Thaw in the refrigerator to prevent condensation on the glaze, then bring to a slightly chilled temperature before serving.

FAQ

Can I make the brownie layer ahead of time? Yes. Bake the brownie layer and cool completely in the pan. Wrap tightly and refrigerate overnight; when ready, proceed with the filling.
What if my buttercream is too soft? Chill the filling briefly in the refrigerator, then re-whip as the recipe instructs.
Why does the recipe call for both creme de menthe and peppermint extract? The creme de menthe gives aromatic, liquor-like depth; the peppermint extract sharpens the mint presence. Together they create a balanced mint note without tasting medicinal.
How do I get clean slices? Warm your knife under hot water, wipe it dry, then slice in a single clean pass. Rewarm the knife between cuts as needed.
Can I use a microwave instead of a double boiler? For the melted chocolate steps you can microwave in short 15–20 second bursts, stirring between bursts. Be cautious—chocolate can seize if overheated. The double boiler is gentler and more forgiving.

Time to Try It

Follow the method steps in order, respect the cooling and chilling times, and you’ll get neat, layered bars with a fudgy base, light mint buttercream, and a glossy chocolate finish. Make them a day ahead for parties or keep them in the fridge for up to four days—either way, the balance of mint and dark chocolate makes them reliably popular.

When you make these, notice how the textures contrast: a slightly underbaked brownie, an airy cooled buttercream, and a firm glaze. Those contrasts are what turn a simple dessert into something people remember. Happy baking—enjoy the clean slices and the satisfying mint-chocolate bite.

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