Sautee onions in a large pot with about 2 tablespoons of olive oil. When onions have become translucent add the two jars of Spaghetti sauce, and can of chopped tomatoes. (I drain the tomatoes and reserve the juice for adding, if too thick)
In a large skillet brown ground beef and Italian sausage until completely cooked, drain fat from meat, and add meat into the large pot with the sauce.
Add chopped pepperoni to the sauce mixture. Add 1 teaspoon of Italian seasonings to mixture.
You can simmer this for 30min, but I prefer to load it into my crock pot and let it go on low for 3~4hrs.
Season w/ S&P at the end because of the spicy meats and add the sliced mushrooms and sliced black olives if you like.
I use this basic sauce for Spaghetti, Lasagna and Italian casserole dishes. It freezes well and gets better in the fridge after a day or two. I often double this recipe, freeze in 1# containers and have a Spaghetti dinner quickly, any time I want it.