Stir everything together until the dough is thick but easy to scoop.
Use a tablespoon-sized cookie scoop to drop dough onto a parchment-lined baking sheet. Press a few extra rainbow chips on top for that classic cosmic look.
Bake at 350°F for 9 to 11 minutes, just until the edges are set and the centers are still soft. Let them cool slightly so they can firm up into chewy, fudgy brownie cookies.