Preheat oven to 350° and grease a 10” cast-iron skillet with cooking spray.

In a large bowl, cream butter and sugars with a hand mixer until light and fluffy. Beat in egg and vanilla. Add flour, cocoa powder, baking powder, food coloring, and salt. Mix until just combined, then fold in chocolate chips.

Spread dough into skillet in an even layer. Top with more chocolate chips and bake 18 to 20 minutes.