Examine all jars for cracks or chips and discard any damaged jars. Wash jars in hot soapy water, rinse thoroughly, and keep hot in a 180°F oven or hot water until ready to fill.
Place new canning lids in a small saucepan, cover with water, and bring to 180°F (do not boil). Keep lids hot until ready to use. Wash rings in hot soapy water and set aside.
Fill your boiling water bath canner with enough water to cover jars by 1-2 inches when submerged. Begin heating water to a rolling boil while preparing jam.
In a large heavy-bottomed pot, combine crushed strawberries and chopped jalapeños. Stir in powdered pectin until completely dissolved, ensuring no lumps remain.
Bring strawberry-jalapeño mixture to a full rolling boil over high heat, stirring constantly. Add sugar and bottled lemon juice all at once, stirring to dissolve completely.
Return mixture to a full rolling boil that cannot be stirred down. Boil hard for exactly 1 minute, stirring constantly. Remove from heat and quickly skim off any foam with a metal spoon
Using a ladle and wide-mouth funnel, fill hot jars with jam, leaving exactly 1/4 inch headspace. Measure headspace with a headspace gauge and adjust if necessary.
Remove air bubbles by running a plastic bubble removal tool around the inside of each jar. Wipe jar rims clean with a damp paper towel to remove any jam residue that could prevent proper sealing.
Center hot lids on jars and apply rings finger-tight only (do not over-tighten). Using jar lifter, place filled jars on canner rack and lower into boiling water, ensuring jars are covered by 1-2 inches of water.
Process in boiling water bath for exactly 10 minutes (adjust processing time for altitude: add 5 minutes for 1,001-6,000 feet, add 10 minutes for above 6,000 feet). Remove jars and cool on a towel for 12-24 hours without disturbing.
