Preheat your oven to 350°F (175°C). It’s crucial to have a hot oven ready for your cookies. This temperature will ensure they bake evenly and develop that beautiful crinkle.
Line 2 baking sheets with parchment paper. This prevents the cookies from sticking and makes cleanup a breeze. Set the lined sheets aside while you prepare the dough.
In a medium bowl, whisk together 1 cup all purpose flour, 1 teaspoon baking powder, 1/2 teaspoon instant espresso powder, and 1/4 teaspoon salt. This dry mix is essential for creating the right texture.
In a medium saucepan over medium heat, melt 6 tablespoons unsalted butter. Watch closely so it doesn’t burn. Once melted, remove the saucepan from the heat.
Stir in 2/3 cup unsweetened cocoa powder and 1 1/2 cups light brown sugar into the melted butter. Mix until combined. The mixture should be smooth and glossy.
Add 2 large eggs, one at a time, whisking well after each addition. This step is important for incorporating air into the dough, giving your cookies that perfect rise.
Now, add the wet mixture to the dry ingredients. Stir gently until just combined. Be careful not to overmix, as that can lead to tough cookies.
Scoop out golf ball-sized rounds of dough and flatten them to about 1/4 inch thick. This is where the magic happens!
Place a Reese's Peanut Butter Cup in the center of each flattened dough piece. Then, scoop another golf ball-sized dough round and place it on top, bringing the edges together to encase the cup. This step is key to achieving that gooey center!
Roll each cookie ball in 1/2 cup confectioners' sugar until heavily coated. This sugar coating will give the cookies a beautiful, sweet exterior once baked.
Place the cookies 2 inches apart on the prepared baking sheets. They will spread while baking, so give them plenty of room.
Bake for 8 to 10 minutes. You want them to look crinkly and slightly set; they’ll continue to firm up as they cool.
Let the cookies sit on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely. This resting period helps them finish baking and solidifies their shape.