The Krabby Patty is the most popular food in the Krusty Krab and the most popular sandwich in Bikini Bottom. It's made a special formula that no one knows except for SpongeBob and Mr. Krabs. The formula is commonly in the hands of attempted robbery, especially from Plankton.
There are 2 contradicting backstories to this formula. In one backstory, the formula has been passed down the Krabs family while in the other one it was accidentally made by Plankton and Mr. Krabs.