Preheat your oven to 350°F (175°C) and grease a 9" x 11" casserole dish.

In a large mixing bowl, combine the white cake mix and cotton candy soda. Beat for about 2 minutes until smooth, adding food dye if desired.

Pour the batter into the prepared dish and bake for 25-30 minutes or until a toothpick comes out clean.

Remove the cake from the oven and cool completely on a wire rack for at least 30 minutes.

While the cake cools, heat 1 cup of cotton candy soda in a saucepan over medium heat until reduced to about 1/4 cup (2 oz). Allow to cool.

In a mixing bowl, beat together softened butter and powdered sugar for 2 minutes until fluffy. Gradually add the cooled soda until combined. Adjust consistency with milk.

Spread the frosting evenly over the cooled cake using an offset spatula.

Sprinkle pastel-colored sprinkles generously over the frosted cake.

Slice the cake into squares and serve to your guests.