Preheat your oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, allowing some overhang for easy lifting of the bars after baking.
In a large bowl, whisk together the melted unsalted butter and granulated sugar until well combined. Add the eggs one at a time, whisking thoroughly after each addition. Stir in the vanilla extract.
In a separate bowl, sift together the all-purpose flour, unsweetened cocoa powder, and salt. Sifting helps avoid clumps and ensures an even texture.
Gradually fold the dry ingredients into the wet mixture using a rubber spatula. Mix just until combined to avoid overworking the batter, which can make the brownies tough.
Fold in the semi-sweet chocolate chips evenly throughout the batter, saving a few to sprinkle on top for that extra chocolatey finish.
Pour the batter into the prepared pan and spread it evenly. Sprinkle the reserved chocolate chips on top. Bake for 30-35 minutes or until the edges are set but the center still looks slightly underbaked—this ensures gooeyness.
Allow the bars to cool completely in the pan on a cooling rack before slicing. This resting time helps the brownies set, making them easier to cut into neat squares.