1 large yellow onion, small dice (about 2 cups)
1 pound sausage
2 Tbsp olive oil
2 tsp chili flakes
2 tsp salt
4 Tbsp tomato paste
2 28-ounce cans tomatoes, chopped (preferably San Marzano) (I pulsed mine in the food processor)
Cook the onions and sausage with the olive oil, chili and salt over a medium heat in a large pot (6 quarts), stirring constantly until the meat is thoroughly cooked and the onions are soft and beginning to brown (about 15 minutes).
Add the tomato paste and continue cooking for five minutes.
Add the canned tomatoes and stir constantly until sauce begins to boil.
Continue cooking for 35 minutes, stirring every four or five minutes so that the sauce does not burn.