The Sponge Cake only appeared in To Save a Squirrel and was mentioned in Blackened Sponge. Patrick had one of these and was going to offer SpongeBob but SpongeBob thought Patrick was going to eat him.
It has bright yellow outside and according to Patrick it has a delicious creamy filling inside.
Patrick: Hey SpongeBob. (his stomach growls)
SpongeBob: Sounds like you're hungry.
Patrick: Oh, boy am I! I'm soooooo hungry, I could eat anything! I could eat an entire sponge..
SpongeBob: Aah-aaahhhhh!!!! (runs away)
Patrick: ...cake. I was just going to share my golden sponge cake with him. It has delicious cream filling too! (eats it)
- It may be a reference to Twinkies.