Lots of different red sauce recipes out there; this one is superb. Been in the family for over 50 years. If you call your red sauce gravy, you gotta try this! Never understood why my grandpa does, but he is insistent. This recipe also freezes well, so feel free. To defrost, the sauce must thaw for about 6 to 8 hours and reheat in a pot.
Pour just enough olive oil into a large pot to coat the bottom; place over medium heat. Cook and stir sweet onion in the pot until it releases some moisture, 1 to 2 minutes. Stir garlic with the onion; cook another 1 minute. Remove pot from heat immediately.
Process the tomatoes in a large food mill using medium holes; grind directly into the pot. Bring the tomato mixture to a light simmer over medium-low heat; season with oregano, salt, and pepper. Allow the mixture to simmer 1 hour, stirring regularly.
Stir basil leaves into the sauce. Simmer 1 hour more, again stirring regularly.