Working with about a pound at a time, quarter the tomatoes and add them to a large stockpot over high heat.

Crush the tomatoes with a potato masher as they heat, bringing them to a boil.

Keep quartering and adding tomatoes, crushing as you go, until all of them are in the pot. Stir often to prevent sticking.

Reduce the heat and simmer uncovered for about 1 hour, until the volume has reduced by half. Stir frequently.

Press the cooked tomatoes through a food mill or fine sieve to remove the skins and seeds. Do not use a blender or food processor.

Return the sieved tomatoes to the stockpot. Stir in the citric acid until fully dissolved and evenly distributed.

Stir in the salt, bay leaves, and garlic clove if using.

Cook uncovered over medium heat until the paste is thick enough to round up on a spoon, about 2 1/2 hours. Stir frequently, and almost constantly toward the end.

As the paste nears done, prepare a boiling water canner, half-pint jars, and two-part lids.

Remove and discard the bay leaves and garlic clove.

Ladle the hot paste into hot half-pint jars, leaving 1/2 inch headspace.

Slide a nonmetallic tool between the paste and the jar wall to release air bubbles, then adjust the headspace.

Wipe the rims clean, center the lids, and screw the bands to fingertip tight.

Process in a boiling water canner for 45 minutes, adjusting for altitude (see notes).

Turn off the heat and let the jars rest in the canner 5 minutes before removing with a jar lifter.

Set the jars on a towel or rack with an inch of space around each, and leave undisturbed 12 to 24 hours.

Remove the rings and check the seals. Refrigerate any jar that didn't seal and use it first.

Label with contents and date. Sealed jars hold quality on the pantry shelf for 12 to 18 months. Refrigerate after opening.