The phrase "separate skillet" refers to using a different frying pan or cooking utensil to cook something separately from the main cooking process. Full definition
In separate skillet heat the pepper sauce over low heat. (mysosofia.com)
You can also do this in two separate skillets if desired. (plateofplants.com)
Cook a steak, a pork chop and some burgers all at once — the revolutionary 360 manufacturing process will make them taste as if they were cooked in separate skillets. (ourfamilyworld.com)