Slice the angel food cake (rectangular) in half lengthwise. Use a round or square cutter to cut out pieces (or cut squares freehand). Cut pieces in half through the middle so that they are the same shape, but shorter.
Spread Nutella on three thin slices of cake. Stack on top of one another and set on a dish in the freezer for 30 minutes, or until the Nutella is very set. Remove from the freezer and ice with soft Cool Whip (may garnish tops with various sprinkles)---then place back into fridge to harden the Cool Whip, about 30 more minutes. (Or you can serve it immediately).
Make the cakes ahead of time, then store in the fridge in an airtight container. To serve, just pull them out 5 to 10 minutes before you need them. THEN CHOW DOWN!