"A thick, black paste that smells like burnt hair."

Void Mayonnaise is made out of void eggs, which come from void chickens duhhhh. Very rarely you can fish out a void mayonnaise from the Witchs Swamp but that really only has a 25% chance.

While you can't purchase it anywhere, it can be sold for 385 gold max.
Everyone I know seems to absolutely hate Void Mayonnaise but Krobus and I really do love it!

Even though it is an awful thick, black, gloopy paste you can't help but really love each bite! I do feel like every time I eat it I lose at least 75 energy. Oh well, sometimes you got to just make a sacrifice for the things you love!!!