Cut tomatoes into quarters, halves, or leave smaller tomatoes whole and lay out onto baking sheets skin side down. (Lining baking sheets with parchment paper helps reduce a messy clean-up later!)
Drizzle tomatoes with olive oil, sea salt, and black pepper. Go light on the oil if intending to hot bath can the sauce.
Roast the tomatoes in an oven pre-heated to 425°F for 35 to 45 minutes. If using multiple pans, rotate halfway through to promote even roasting.
Optional: If you have more tomatoes than will fit in your oven, lightly simmer the remaining tomatoes in a pot for the entire time the roasted tomatoes are in the oven. Choose a pot that is large enough to accommodate the stewed and roasted tomatoes together, once they are added after roasting.
Once the tomatoes are finished roasting, add to a pot over medium low heat or combine with the tomatoes simmering on the stove top and simmer to reduce to your desired consistency.
Blend the tomato mixture with immersion blender directly in the pot, or add mixture to blender in batches, and blend until creamy and smooth.
Once the roasted tomato sauce is blended and reduced to your desired thickness, remove from heat and let the sauce cool.
Pack the sauce in freezer safe containers (such as wide-mouth jars) for storage in the freezer, or use fresh within one week.
To hot-bath can the sauce, add and thoroughly stir in either 2 tablespoons of bottled lemon juice or 1/2 tsp of citric acid per quart of tomato cause. For pint jars, half that amount. Follow the canning times based on jar size and elevation in the chart provided in this article.