Step 1: Make the Brown Butter: Melt ½ cup unsalted butter over medium heat until it turns deep amber with brown specks, about 5-7 minutes. Set aside to cool slightly.

Step 2: Prep Brownie Cookies: Combine melted butter and ½ cup chocolate chips in a bowl. Melt together, then whisk in cocoa powder, dark brown sugar, and egg. Fold in flour, baking powder, and salt.

Step 3: Chill Dough: Transfer brownie dough to a bowl, cover with plastic wrap, and refrigerate for at least 30 minutes.

Step 4: Prep Chocolate Chip Cookies: Whisk together brown butter with granulated and dark brown sugar. Add egg and vanilla extract, then fold in flour, baking powder, baking soda, and chocolate chips.

Step 5: Combine Doughs: Scoop portions of both doughs and alternate forming marbled balls on a baking sheet. Refrigerate again for at least 30 minutes.

Step 6: Bake: Preheat oven to 350°F (175°C). Bake marbled dough balls for 12-14 minutes until edges are golden. Cool on the sheet before transferring to a wire rack.