Instructions

• Preheat oven to 350°F (175°C). Line an 8-inch square baking pan with aluminum foil, leaving some overhang to lift the bars out later, and spray the foil with cooking spray; set the pan aside.
• In a large bowl combine 1 cup all-purpose flour, 1/3 cup confectioners’ sugar, and 1 tablespoon cornstarch. Stir to distribute evenly.
• Add 1/2 cup (1 stick) unsalted butter, extremely soft, and 1 teaspoon vanilla extract. Use a pastry cutter, two forks, or your fingertips to cut the butter into the dry ingredients until the mixture is sandy and crumbly.
• Turn the crumbly mixture into the prepared pan. Using your fingertips or a spatula, press and hard-pack the crumbs into an even, flat crust layer. Pierce the crust evenly about a dozen times with a fork to allow steam to escape.
• Bake the crust for 12 to 13 minutes, or until it has just set and is no longer raw-looking. The crust should still be pale (not browned). Remove from the oven and set aside while you make the filling.
• For the peanut butter filling: place 2 tablespoons unsalted butter (melted) in a medium microwave-safe bowl and heat on high about 30–60 seconds until melted. (If your melted butter is already measured as “melted,” proceed to the next step.)
• Add 1 heaping cup creamy peanut butter (not natural), 1/2 cup confectioners’ sugar, 1/2 teaspoon vanilla extract, and 1/4 teaspoon salt (optional and to taste) to the melted butter. Stir until the mixture is smooth and fully combined.
• Spread the peanut butter filling evenly over the warm crust using a spatula or offset knife. It is fine (and helpful) to spread while the crust is still warm.
• For the chocolate layer: place 1 heaping cup (about 8 ounces) semi-sweet chocolate chips and 2 tablespoons vegetable shortening (optional, recommended) in a medium microwave-safe bowl. Heat on high for 1 minute, stop and stir, then continue heating in 15-second bursts, stirring between bursts, until the chocolate is fully melted and smooth.
• Pour the melted chocolate over the peanut butter layer. Gently tilt or shake the pan so the chocolate spreads, then smooth very lightly with an offset spatula or knife to an even layer.
• Cover the pan with a sheet of foil and allow the bars to set at room temperature for at least 4 hours (or overnight) until the chocolate is firm. Alternatively, refrigerate the pan for at least 3 hours to speed setting (refrigeration can make chocolate appear slightly dull but does not affect flavor).
• If refrigerated, let the pan sit at room temperature for a few minutes before slicing to reduce the chance of the chocolate cracking. Use the foil overhang to lift the bars from the pan, then cut into bars. For cleaner slices, use a sharp knife warmed under hot water and wiped dry between cuts.