Preheat oven to 325°F.

Heat a saucepan over medium-low heat and add butter. Whisk constantly until brown bits appear on the bottom (about 5 minutes), then remove and let cool completely.

Add butter to a large bowl with sugars and whisk until completely smooth.

Add in egg and egg yolk, whisking until combined, then add in vanilla.

Separate the dough into two halves.

In one bowl, add 1 cup of flour, 1/4 teaspoon baking soda and a pinch of salt, then mix until a dough forms, using your hands if necessary. Fold in half of the chocolate chips. Set aside

In the second bowl, add remaining flour and baking soda, cocoa powder and a pinch of salt, mixing until a dough forms. Fold in chocolate chips.

Roll each dough into 12 balls (about an inch thick) so you end up with 24.

Press two balls of different doughs together lightly, making 12 double cookies.

Place dough chocolate side down on a non-stick baking sheet about 1 1/2-2 inches apart.

Bake for 10-12 minutes, or until cookies are a little soft in the middle and golden on the edges. Let cool completely.