Brown Butter Chocolate Chip + Brownie Cookies (Brookies)

1. Brown butter and let cool slightly.
2. Prepare the chocolate chip cookie dough by combining the browned butter, sugars, egg, egg yolk, and vanilla extract. Gradually mix in the flour, cornstarch, baking soda, and salt until just combined, then fold in the chocolate chips.
3. Prepare the brownie dough by creaming together the unsalted butter and sugars. Beat in the egg and vanilla extract. Mix in the cocoa powder, flour, baking soda, and salt until just combined, then fold in the chocolate chips.
4. Chill both doughs for 10 minutes.
5. Preheat oven to 350°F (175°C).
6. Scoop equal portions of each dough (chocolate chip and brownie) and press them together into one ball, marbling them slightly if desired.
7. Bake at 350°F for 8–9 minutes, or until the edges are set and the centers are slightly soft.
8. Cool on the baking sheet for a few minutes before transferring to a wire rack. Enjoy!