Add 1 tbsp lemon juice and 1/2 tsp salt in a hot pint jar, or 2 tbsp lemon juice and 1 tsp salt in a hot quart jar.
Wash, peel and quarter tomatoes, removing cores and bruised or discolored portions. Place tomato quarters in large saucepan. Bring to a boil. Boil gently for 5 minutes, stirring constantly. Using a hand blender, puree the tomatoes. Put puree into the prepared jars. Put hot lids and rings on jars. Process in hot water bath 35 mins for pint jars, 45 mins for quart jars.