Preheat oven to 350°F. Grease a 13" x 9" metal baking tin. Line with parchment, leaving the paper slightly long to create a handle to grab the brownies out. Grease the top of the parchment as well.
Combine eggs, cocoa, salt, baking powder, and espresso powder in a bowl. Mix on medium-high for 2-3 minutes.
4 eggs, 2 egg yolks, 126 g cocoa powder, 1 1/2 teaspoons salt, 2 teaspoons baking powder, 1 teaspoon espresso powder
Meanwhile, heat butter, sugars and vanilla on stovetop or in microwave until butter is melted and mixture is hot, stirring regularly.
255 g unsalted butter, 250 g sugar, 1 tablespoon vanilla extract, 266 g brown sugar
Slowly stir butter mixture into egg mixture.
Stir in flour and chocolate chips
240 g all-purpose flour, 300 g chocolate chips or chunks
Pour 1/2 of the brownie batter into prepared tin. Spread evenly. Top with an even layer of oreos. Pour in remaining batter and smooth evenly.
48 Oreos
Crumble pieces of remaining oreos on top.
Bake for 35-38 minutes until a toothpick comes out with just a few crumbs (but no liquid batter).
Cool completely in tin before cutting into 24 squares.