Bake or buy a cake layer and let it cool completely
Line a springform pan or cake pan with plastic wrap or parchment paper
Soften ice cream until spreadable
Place one cake layer in the pan
Spread a thick layer of ice cream over the cake
Add another cake layer if desired
Freeze until firm
Add whipped cream, frosting, or ganache on top
Decorate with sprinkles, chocolate, fruit, or candy
Freeze again until ready to serve
Remove from the pan and slice with a warm knife