Where you see a saucepan sitting on top of the dome cover or the inverted combination unit, it may not have started out there. You must begin cooking most raw vegetables in a saucepan on a burner at medium heat. Once the cover of the pan is hot to touch and the cover spins freely on a cushion of water you can place the saucepan on the dome cover to finish cooking. Precooked foods such as canned vegetables or thawed frozen vegetables are the exceptions. You can start them out on top of a stack.