It has a bright yellow exterior, and, according to Patrick, has a delicious creamy filling inside, which is seen in "InSPONGEiac."
In SpongeBob vs. The Big One: Beach Party Cook-Off, they appear to be part of SpongeBob with green frosting on them.
Role in series
When SpongeBob asks Jack M. Crazyfish if he's ready to get crazy, Jack responds "You bet your frosting, sponge cake!"
"To Save a Squirrel"
Patrick deems himself so hungry that he could eat a sponge cake. SpongeBob runs away in horror upon the syllable pause in between the words "sponge" and "cake," after which it turns out that Patrick just wanted to share a sponge cake with him.
Patrick imagines SpongeBob as a sponge cake and bites his hand.
Role in SpongeBob vs. The Big One: Beach Party Cook-Off
Sponge cakes appear as a dessert item on the menu. To make one, the player has to juice, melt, deep fry, and paint in that order.
In "To Save A Squirrel," the sponge cake looks exactly like a Twinkie.
The one shown in "InSPONGEiac" appears more closely to what an actual Sponge cake looks like.