In a large casserole pot, heat oil over medium high heat.
Add onion and garlic and saute until soft and translucent, about 2 minutes.
Add celery and carrots and season with salt and pepper.
Saute until all the vegetables are soft, about 5 minutes.
Add tomatoes, basil, and bay leaves and simmer covered on low heat for 1 hour or until thick.
Remove bay leaves and check for seasoning.
If sauce still tastes acidic, add unsalted butter, 1 tablespoon at a time to round out the flavors.
Add half the tomato sauce into the bowl of a food processor.
Process until smooth.
Continue with remaining tomato sauce.
If not using all the sauce, allow it to cool completely and pour 1 to 2 cup portions into freezer plastic bags.
This recipe will yield 6 cups of tomato sauce and will freeze up to 6 months.