Prepare your canning station: wash jars in hot soapy water, rinse, and keep them hot in the canner at 180°F. Place lids in a small saucepan of hot water (not boiling) to soften the seals.

Peel the tomatoes: score a small X on the bottom of each tomato, blanch in boiling water for 45-60 seconds until the skin splits, then plunge into an ice water bath. Slip off the skins, core, and chop the tomatoes into 1/2-inch pieces. You need 8 cups of chopped tomatoes.

In a large stainless steel or enamel pot (not aluminum, which reacts with acid), combine the chopped tomatoes, onions, bell peppers, jalapeños, garlic, lemon juice, salt, cumin, black pepper, and sugar if using. Do not add cilantro now — it will turn bitter and dark during processing.

Bring the mixture to a boil over medium-high heat, stirring frequently to prevent sticking. Reduce heat and simmer for 10 minutes, stirring occasionally. The salsa will thicken slightly and the vegetables will soften.

During simmering, prepare the water bath: fill the canner about half full with water, bring to a boil. Place the hot jars on a clean towel.

Ladle the hot salsa into the hot jars using a wide-mouth funnel, leaving 1/2-inch headspace. Remove air bubbles by sliding a non-metallic spatula (or chopstick) around the inside of each jar. Wipe the jar rims with a clean, damp paper towel. Center a lid on each jar, then screw on the band until fingertip-tight.

Using a jar lifter, place the filled jars into the boiling water bath, ensuring they are covered by at least 1 inch of water. Cover the canner, bring back to a full rolling boil, and process for 15 minutes (adjust for altitude: add 5 minutes if 1,001–3,000 ft, 10 minutes if 3,001–6,000 ft).

After processing, turn off the heat, remove the canner lid, and let the jars sit for 5 minutes. Then lift them out onto a thick towel or wooden board, leaving at least 1 inch of space between jars. Do not tighten the bands.

Let the jars cool undisturbed for 12-24 hours. You will hear the satisfying ping of lids sealing. After cooling, press the center of each lid — it should be concave and not flex. Any unsealed jars should be refrigerated and used within 2 weeks.

Label the sealed jars with the date and store in a cool, dark place. For best quality, use within 12-18 months.