Idiom
cook up somethingcook up (something)
to invent something to produce a result you want.Freddy cooked up a great story so that Jane wouldn't know she was on her way to a surprise party for her birthday.
Usage notes: often cook up means to invent something that is dishonest or illegal:
I'd like to find out who cooked this scheme up.
Etymology: based on the idea of cooking food to make a meal