Heat olive oil in a large pot. I use a cast iron dutch oven, but any large pot works.
Sauté onion for about five minutes.
If you want to add mushrooms, add to pot, and sauté for a few more minutes.
Add the garlic, and sauté for about 30 seconds, or until fragrant.
Open the tomato cans, and smash them with your fingers as you add them to the pot. Pour remaining sauce into pan.
Add fresh oregano and basil to pot.
Add nutmeg, anchovy paste, red pepper flakes, and salt to pot and stir well.
If you are adding meatballs or brussels sprouts (or both!), add them to the pot.
Let sauce simmer for an hour or two, stirring occasionally.