Step 1. Slice tomatoes and place in large pot. Boil until they are soft, approximately 15-20 minutes.
Step 2. Strain cooked tomatoes and place sauce in clean pot. Bring sauce to boil again on medium low heat for another 45 minutes. This will cause any extra liquid to evaporate, making the tomato sauce thicker.
Step 3. Boil jar lids and rings for 3 minutes to sterilize. Pour hot sauce into clean jars. Close with sterilized lids. Keep jars together, covered, until the lids pop indicating that the jars are sealed. No further processing is needed. Store in cool, dry place.