Cartman Burger was a business created by Cartman in the episode "Ass Burgers".
Background
Cartman originally made burgers in an attempt to give himself Asperger's Syndrome, having mistaken "Asperger's" as "Ass Burgers". Kyle Broflovski then tried one and spread the word after discovering its delightful flavor. However, the flavor produced was made by Cartman putting the burgers in his underwear.
Cartman later created a business selling the burger, located in front of his house. Restaurant franchises believed Cartman had invented a superior burger by combining all of their flavors by infusing them into a gas. They sent Stan Marsh to obtain the secret recipe. Kyle would not tell him and he almost got shot in the head and all the customers were scared away. The business went bust after Kyle discovered the shocking trade secret.