The easiest way is in a cake pan! We use a 9″ pan but an 8″ round would work, too. Pressing the dough into a pan, rather than freehand it on a baking sheet, ensures that it’ll bake evenly.
1 c. butter, softened
3/4 c. packed brown sugar
3/4 c. granulated sugar
2 large eggs
2 tsp. pure vanilla extract
2 2/3 c. all-purpose flour
1 tsp. baking soda
1/2 tsp. kosher salt
2 c. chocolate chips (plus more for sprinkling)
1/4 c. rainbow sprinkles (plus more for sprinkling)
1 c. vanilla frosting
Preheat oven to 350° and line a 9″ round cake pan with parchment paper. Grease with cooking spray. In a large bowl using a hand mixer, beat butter and sugars until light and fluffy. Add eggs, one at a time, beating well between each addition. Stir in vanilla. Add flour, baking soda and salt and mix on low until just combined. Fold in chocolate chips and rainbow sprinkles.
Press cookie dough into an even layer in the prepared pan. Top with more chocolate chips and sprinkles, if desired. Bake until the cookie is golden, about 35 to 40 minutes. Let cool in pan for 15 minutes then transfer cake to a cooling rack to cool completely.
Transfer frosting to a piping bag fit with a large star tip. Pipe frosting around the edge of the cooled cookie cake. Slice into wedges.