The day before you actually make the sauce, you will need to prepare your tomatoes. Wash and core your tomatoes. Cut them into chunks. Mix them, in a large bowl, with the salt. Place your tomatoes in large colanders, set over large bowls, to drain. Allow them to drain this way for 12 to 14 hours. However, if you don’t have enough colanders to drain all of your tomatoes, it’s fine. Leave them in the buckets as is. You’ll simply add more time to the heating process, to get rid of the excess liquid.
After the draining time, you will cook your tomatoes. In a large saucepan add about 1/4 inch of olive oil. Next, add the tomatoes to the pot and cook them, over medium heat until heated through. Stir regularly. Remove from heat, and let cool slightly.
Next, you will pass the heated tomatoes through the food mill, according to your food mill’s instructions. You will see that the juice and pulp of the tomatoes gets separated from the skin and seeds. After you collect enough skin and seeds, pass these through the food mill again; you will be surprised to see how much more liquid can get squeezed out of there.
Once you have passed all of the tomatoes through the food mill, it is time to cook your tomato sauce. Add the lemon juice to your tomato sauce. Cover the bottom of your pot with enough vegetable oil to come up about 1/2 inch, before adding the pureed tomatoes to the pot. Boil your sauce over medium heat for about 45 minutes to 1 hour, stirring regularly. This will help thicken your sauce as the excess water will evaporate.
While your sauce is cooking, sterilize your canning jars by inserting them in boiling water for about 10 minutes.
Once your sauce is cooked, add one sprig of basil per sterilized jar. Pour the tomato sauce into the jars, leaving about 1 inch of head space between the top of the tomato sauce and where the screw top begins on the jar. Fill this space with olive oil. Place the canning disks and bands onto the jars and insert them into the water bath for about 20 minutes. Remove carefully the jars from the water bath and allow to cool. Check each lid to be sure that the can has been properly sealed. If it has not, store your tomato sauce in the fridge and use within a few days.
Store your canned tomato sauce in a cool dark place. It can be used in a number of different recipes.