Lay a kitchen towel on the countertop. Use the jar lifter to remove warm jars from the canner, drain, and line up on the towel.
Add 1/8 teaspoon of citric acid or 1/2 tablespoon of bottled lemon juice to each jar.
Ladle the warm tomato sauce into the jars leaving 1/2-inch headspace.
Stir the jars with the bubble popper to release air bubbles. Clean the jar rims. Place the lids on the jars and screw on the band until it is fingertip tight.
Use the jar lifter to place the jars back into canner. Adjust the water level so it is at least one inch above the tops of the jars.
Cover the canner and bring to a rolling boil over high heat. Once water boils, set a timer and boil for 15 minutes at altitudes of less than 1,000 ft. (adjust processing time for your altitude if necessary).
When processing time is complete, turn off heat, and let the canner to cool down for about 10 minutes.
Lay a kitchen towel on the counter. Remove the jars from the canner using the jar lifter and place on the towel. Allow the jars to cool for 12 hours.
After 12 hours, check to be sure jar lids have sealed by pushing on the center of the lid. The lid should not pop up. If the lid flexes up and down, it did not seal. Refrigerate jar and use up within a few days.
Remove the screw on bands and wash the jars. Label and date the jars. Store your jars in a cool, dark place and use within 12 months. Yields about 12 half-pint jars of pizza sauce.