It's a colloquialism with no particular meaning. Jimmy cooked burgers and steaks would have done just as well.
Note that "cook up" can have other slang meanings: cook up - Wiktionary
Max and Jimmy invited Claire over for a Mid-Autumn Festival barbucue. Max tried to impress Claire with his knowledge about the holiday while Jimmy cooked up burgers and steaks.
What does cooked up refer to, especially up, in the above condition? Thanks.
Thanks, Anglika, for your help.