Start by prepping all your ingredients.
Chop the onion and mince the garlic.
If you bought whole mushrooms, wash and slice them.
Mince your herbs. You can mince all of them together, as they will go into the pot together. I like to use fresh oregano, basil, and Italian flat leaf parsley.
Add a little olive oil to a big pot. I like to use my cast iron dutch oven. Sauté the onions until they start to turn transparent, about five minutes.
Then, add the garlic and sauté for about 30 more seconds.
Add the mushrooms, and sauté about five more minutes.
Add salt and pepper.
Deglaze the pot with about 1 cup red wine. I use whatever I have on hand, but you can also buy a cheap bottle to use. My favorite varietals for tomato based sauces are the heavy ones. Cabernet Sauvignon is my favorite to use, but a Cabernet Franc or other wine that is high in tannins will work, too.
Add 2 cans San Marzano tomatoes. Open the cans, and add the tomatoes one at a time, crushing each one with your hands until they fall through your fingers.
If you would like a touch of heat, add 2 teaspoons red pepper flakes.
Throw your minced herbs into the pot.
Add about 2 teaspoons sugar and a dash of nutmeg.
Taste, and add salt as needed.
Bring to a low boil, then turn down the heat, cover, and let the pot simmer for a couple hours, stirring occasionally.
You can make the sauce as early as you wish. It can simmer all day, if you want.