Prepare canner, jars and lids
In large stainless steel saucepan, combine 1 cup of tomato puree, onion, celery, carrot and garlic. Bring to a boil over medium-high heat, stirring frequently. Reduce heat, cover and boil gently until vegetables are tender, about 5 minutes.
Keep mixture boiling and add remaining tomato puree, 1 cup and a time, stirring frequently. Stir in lemon juice, salt, black peper, and hot pepper flakes. Increase heat to high, bring to a full rolling boil. Boil hard, stirring frequently, until mixture is reduced by 1/3 (about 15 minutes).
Ladle hot sauce into hot jars, leaving 1/2 inch headspace. Remove air bubbles and adjust headspace if necessary. Wipe rim. Place lid and tighten band to fingertip-tight.
Place jars in canner, all jars completely covered with water. Bring to a boil and process 35 minutes. Remove lid, wait 5 minutes, then remove jars, cool and store.