Heat oven to 350°F. Line an 8-inch square pan with parchment, leaving overhang.
Whisk melted butter, granulated sugar, and brown sugar until glossy and combined.
Whisk in the beaten eggs and vanilla until the mixture looks thick and smooth.
In a bowl, combine flour, cocoa, salt, baking powder, and espresso powder.
Fold dry ingredients into the wet mixture just until streaks disappear. Do not overmix.
Stir in chocolate chips and most chopped cookies, reserving a handful for topping.
Spread batter into the pan. Scatter remaining cookie pieces on top and press lightly.
Bake 26–30 minutes, until edges are set and a toothpick shows moist crumbs.
Cool in the pan on a rack for 30 minutes. Lift out and cut into squares.