Wash all mason jars, lids, and bands with hot soapy water and rinse thoroughly. Fill your water bath canner with water and bring it to a simmer while you prepare the recipe.

Rinse the jalapeños under cold water and pat them dry with a clean kitchen towel. Using a sharp knife, carefully slice off the stem end and slice the peppers into thin rings, removing most of the seeds and white membrane as you go to control the heat level.

Pour the sugar, vinegar, mustard seeds, celery seeds, turmeric, and black peppercorns into a large stainless steel pot. Stir well to combine and ensure the sugar begins to dissolve slightly before heating.

Place the pot over medium-high heat and bring the mixture to a rolling boil, stirring occasionally to help the sugar dissolve completely.

Carefully add the sliced jalapeños and garlic to the boiling liquid, stirring gently to submerge them. Return the mixture to a boil and let it cook for 4 to 5 minutes so the peppers soften slightly while retaining some crunch.

Stir in the pickling salt and reduce the heat to medium, allowing the mixture to simmer gently for another 5 to 8 minutes.

Using a canning funnel, carefully ladle the hot pepper mixture into sterilized jars, leaving about 1/2 inch of headspace at the top. Use a bubble remover tool to gently release any air pockets trapped in the jar by sliding it around the inside edges.

Wipe the rim of each jar with a damp, clean cloth to remove any spilled syrup or residue. Center the hot lid on each jar and screw the band down fingertip-tight, not cranked hard, so air can escape during processing.

Using a jar lifter, carefully lower each filled jar into the simmering water bath, ensuring they are covered by at least 1 inch of water. Bring the water to a rolling boil and process the jars for 10 minutes, adjusting time upward if you live at a higher altitude.

Remove the jars from the canning pot using the jar lifter and place them upright on a clean kitchen towel, spacing them apart so air can circulate. Allow them to cool completely, undisturbed, for 12 to 24 hours. You will hear the satisfying pop of the lids sealing as they cool. Once cooled, press the center of each lid gently; if it does not flex or make a clicking sound, it has sealed properly.