1. Add 226 grams of butter to a small saucepan over medium heat, stirring occasionally, until it starts to fizz slightly. Continue to stir until you see the milk solids turn a toasty brown.
2. Divide the brown butter evenly into two large bowls. Since moisture has cooked off during the browning process, each bowl should have about 100 grams of butter.

To make the brownie cookie:

1. Add 1 tablespoon of milk and whisk to temper the brown butter. Let it cool for a few more minutes. Once cooled, whisk in 1 egg, 118 grams of brown sugar and 50 grams of granulated sugar until combined.
2. Add 175 grams of all-purpose flour, 2 tablespoons of cocoa powder, 1 1/2 teaspoons of baking powder and 1/4 teaspoon of kosher salt to the bowl. Mix until just combined.

To make the peanut butter cookie:

1. Add 1 tablespoon of milk and whisk to temper the brown butter. Let it cool for a few more minutes. Once cooled, whisk in 1 egg, 118 grams of brown sugar and 50 grams of granulated sugar until combined. Whisk in 75 grams of creamy peanut butter until combined.
2. Add 183 grams of all-purpose flour, 1 1/2 teaspoons of baking powder and 1/4 teaspoon of kosher salt to the bowl. Mix until just combined.
3. Split 113 grams of chocolate evenly between the cookie doughs.
4. Scoop out 3 tablespoons of each dough and roll them together into a smooth, marbled ball in your hands. Repeat this until you have 10 large cookies.
5. Place the cookie dough balls on a parchment-lined baking sheet and chill in the refrigerator while you preheat the oven to 350°F.
6. Bake for 10-12 minutes. The key is to remove the cookies before they look fully done. They will continue to "cook" outside of the oven, so this method helps them maintain the chewy texture.
7. Let cool and serve!