• Preheat your oven to 350°F. Line a 9"x13" brownie pan with non-stick foil.

Brownie Batter

• Place the chocolate, butter and espresso powder in a medium, microwave safe bowl. Use the melt chocolate function on your microwave, or heat for 1 minute, stir, and continue to heat in 30 second intervals (stirring in between) until fully melted and smooth. (You can also use a double boiler for this step)
  226 g bittersweet chocolate, 165 g butter, 1/2 tsp espresso powder
• In a small bowl, whisk together the flour, cocoa powder and salt. Set aside.
  80 g flour, 16 g cocoa powder, 2 g salt
• In a large bowl, on low speed, beat together the eggs, egg yolk, sugar, brown sugar and vanilla until the sugar is dissolved and the mixture is a thick, glossy, syrup. Avoid whipping too much air into the mixture.
  3 eggs, 1 egg yolk, 134 g sugar, 74 g brown sugar, 15 ml vanilla
• Stir the melted chocolate mixture into the egg and sugar mixture until uniform in color and consistency.
• Add the flour mixture and fold just until no more dry ingredients are visible.
• Fold in the blond chocolate chips and semisweet chocolate chips. Set the brownie batter aside.
  160 g blonde chocolate chips, 80 g semisweet chocolate chips

Cookie Batter

• Add the butter and dry milk powder to a medium saucepan. Cook over medium low heat until the milk solids are golden brown and have a rich, nutty aroma. Immediately transfer to a large mixing bowl,
  224 g butter, 16 g dry milk powder
• Add the brown sugar, sugar, vanilla and salt to the browned butter, whisk to combine and start the sugar melting. Let rest until cooled to room temperature.
  165 g brown sugar, 150 g sugar, 15 ml vanilla, 2 g salt
• Beat in the eggs and egg yolks on low speed until the sugar is dissolved and the mixture is thick and syrupy.
  2 eggs, 1 egg yolk
• Stir in the flour and semisweet chocolate chips until no dry ingredients are visible and the chocolate chips are evenly distributed.
  240 g flour, 240 g semisweet chocolate chips

Assembly

• Add alternating scoops of brownie batter and cookie batter to your prepared pan attempting to get roughly equal distribution of the two batters. Use a butter knife to lightly swirl the batters together (the batters may clump and drag a bit rather than smoothly swirling, that is ok). Gently tap and shake the pan to settle the batter more evenly in the pan.
• Place the pan in the preheated oven for about 34 minutes. The edges will be set, the top will be dry and slightly glossy, the middle will appear a little loose if you shake the pan - be careful not to overbake or the brookies will be dry.
• Allow the brookies to cool completely before slicing into 24 large or 40 small bars.