1. Bring a large dutch oven or stockpot of water to a boil over high heat. Fill a mixing bowl with ice and water and set next to stove.
2. Core out the stems from the tomatoes and slice a shallow "X" in the bottom of each fruit. Working in batches, drop several tomatoes into the boiling water. Cook until you can see the skin starting to wrinkle and split, 45-60 seconds, then lift the tomatoes out with a slotted spoon and plunge them into the ice water. Continue with the rest of the tomatoes, transferring the cooled tomatoes from the ice water to another mixing bowl as they cool. When finished, use your hands or a parting knife to strip the skins from the tomatoes. Discard the water used to boil the tomatoes.
3. Working in batches, pulse the tomatoes in the food processor. Pulse a few times for chunkier sauce, or process until smooth for a pureed sauce. Transfer each batch into dutch oven or stockpot.
4. Bring the tomato sauce to a simmer over medium heat. Continue simmering for 30-90 minutes, stirring occasionally, until the sauce reaches the taste and consistency that you like.
5. When finished cooking, stir in the lemon juice or vinegar and salt. (a quarter cup is necessary to ensure a safe level of acidity for canning). Add more lemon juice or vinegar to taste.
6. Complete water bath.
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