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. OMIT 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 - until they develop a brown tinge. If using multiple pans, it may take longer (up to an hour). Rotate trays 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, carefully transfer them to a large pot on the stovetop (combine with the optional stewed tomatoes). Blend with immersion blender directly in the pot, or add mixture to a classic blender in batches, and blend until creamy and smooth.
If needed, simmer the sauce to further reduce until it reaches 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.