Preheat your oven to 325˚F. Arrange the tomatoes cut side up on baking sheets, and roast in a preheated oven until they are mostly dry and the skins loosen and slip off easily, about 1 hour. Remove the tomatoes from the oven and set aside to cool.

While the tomatoes are roasting, prepare the jalapenos, onions, and garlic. Add them to a prep bowl and set aside. Be sure to wear gloves to protect your hands from the hot pepper juices.

Wash the jars, lids, screw bands, and canning tools in hot soapy water and rinse well.

Place the water bath canner on the stove, add the jar rack, place jars upright on the rack, and add water to cover the jars. Bring the canner to a simmer (180˚F) for at least 10 minutes, and keep warm.

Once the tomatoes are cool enough to handle, slip off the skins. Then add the tomatoes, jalapenos, onions, garlic, salt, and pepper to a food processor and puree until your desired consistency, chunky or smooth.

Pour the puree into a large saucepot and bring to a boil. Then, reduce the heat and let it simmer, stirring frequently, until heated through, about 5 minutes.

Spread a towel on the counter. Use the jar lifter to remove a warm jar from the canner. Drain the water back into the canner and place it on the towel. Keep the remaining jars in the canner so they stay warm.

Run the bubble popper through the jar to release air bubbles. Adjust the headspace again if needed to maintain 1/2-inch.

Wipe the rim with a damp paper towel. Center a lid on the jar, and screw on the band until it is fingertip tight. Place the jar in the canner and repeat until all the jars are filled.

Once the filled jars are all in the canner, adjust the water level to two inches above the jar tops.

Cover the canner and bring it to a rolling boil over medium-high heat. Once it boils, set a timer and process half-pints in a boiling water bath canner for 35 minutes at altitudes of less than 1,000 ft. Adjust processing time for your altitude if necessary. (See notes)

When the processing time is complete, turn off the heat, remove the cover, and let the canner cool down and settle for 5 minutes.

Spread a dry kitchen towel on the counter. Use a jar lifter to remove the jars one at a time from the canner. Keep the jars upright and place them on the towel spaced several inches apart. Do not tighten ring bands or test the seals yet. Let the jars sit undisturbed for 12 to 24 hours to cool.

After the jars have cooled for at least 12 hours, check to be sure the 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. Place the jar in the refrigerator, and use within 2 weeks.

Remove the ring bands, wash, label, date the jars, and store in a cool, dark place between 50 to 70˚F for 12 to 18 months. Once the jar is open, store in the fridge and use it within 2 weeks. Yields about 4 half pints.