Preheat oven to 400℉.
Divide the tomatoes, onions and garlic cloves between two rimmed sheet pans.
Drizzle with olive oil and sprinkle with Italian seasoning, salt and black pepper.
Gently toss the mixture to evenly coat the tomatoes in the oil and seasonings.
Bake for 30-40 minutes or until the tomato are turning a golden brown and the tomato skins are beginning to come off.
Remove from the oven and let cool for a few minutes. Remove the skins, if desired.
Pour the mixture into a blender or a food processor and blend until smooth.
Season to taste & enjoy warm over cooked pasta.
Let the blended sauce cool completely.
Pour into labeled freezer bags, remove excess air, close tightly and freeze.
