In large skillet, saute chopped onion, sliced eggplant, sliced zucchini in olive oil and butter until onions are translucent (about 15 minutes), then add garlic and saute for an additional minute.
Add sauce and simmer on low heat for about 2 hours, mixing every 30 minutes or so.
Layer large casserole dish first with half the sauce mixture, ricotta cheese, half the parmesan, romano and mozzarella cheese, then another layer of the sauce mixture, parmesan, romano and mozzarella cheese.
Bake on 350 for 30-40 minutes until bubbling at the sides and cheese is slightly browned on top.
