Preheat oven to 350°F (180°C) and line a baking sheet with parchment paper. Cream butter with granulated and brown sugars until light and fluffy. Add eggs one at a time, mixing well.

In a separate bowl, whisk together flour, cocoa powder, and baking powder. Stir dry mixture into creamed batter until just combined.

Fold in half of the chocolate chips using a spatula to create a thick dough. Allow batter to rest for a few minutes.

Divide dough into two portions. Keep one as cookie dough and mix remaining chocolate chips into the second for brownie flavor.

Drop alternating spoonfuls of brownie batter and cookie dough on the baking sheet. Swirl gently with a toothpick.

Bake for about 12 minutes until edges are set and centers are soft. Cool on baking sheet for 5 minutes before transferring to a wire rack.