Preheat oven to 350℉.

Place 1 cup of the chocolate chips in a plastic bag and use a rolling pin to break them down into small pieces (set the other 1 cup of unchopped chocolate chips aside).

In a small microwave-safe bowl, melt the unsalted butter (1 cup) for 20-30 seconds until JUST melted.

Transfer butter to a larger bowl, then add in granulated sugar and light brown sugar and use a spatula to stir until combined.

Add in eggs and vanilla extract, then mix.

Next, add in baking soda, baking powder, and salt and mix again.

Add in all-purpose flour and mix until all the flour disappears into the dough.

Add the 1 cup of chopped chocolate chips and 1 cup of whole chocolate chips into the dough and mix.

Grease a 13x18" half sheet metal cookie cake pan and press dough into an even layer in pan.

Bake at 350℉ for 16-18 minutes - do NOT overbake.

Remove from oven and place entire pan on a cooling rack. Allow the cookie cake to cool completely before removing.

Using a large star piping tip, pipe around the edges then immediately add sprinkles.

Beat the softened unsalted butter on medium-high speed for 2 minutes until smooth.

Turn the mixer to low speed then add the powdered sugar ¼ cup at a time.

Add vanilla extract and salt and turn mixer to medium speed.

One tablespoon at a time, add milk. Beat on high for 2-3 minutes until creamy.

Frost the cooled cookie cake and cut into 24 squares.