Line a 9-inch round pan with plastic wrap. Fill with softened ice cream of your choice (I used Cookies and Cream). Freeze for 2-3 hours until set.
Meanwhile, prepare and bake the cake mix of your choice (I used Funfetti) according to package directions for two 9-inch round baking pans. Let cake cool for 5-10 minutes in the pan before removing to wire racks to cool completely.
Place one cake layer on a serving plate. Top with ice cream layer (removing the plastic wrap). Then invert the second cake layer on top of ice cream.
Cover the top and sides of the cake with Cool Whip and sprinkles. Freeze another 2 hours until set.
Note: Remember to remove the cake from the freezer for a while (20-30 minutes) before trying to cut the cake. Sometimes cutting the cake is the most difficult part.