Rinse jalapeños under cool water. Slice into ¼-inch rounds. Wear gloves if you're sensitive to heat.

In a large pot, combine sugar, apple cider vinegar, turmeric, celery seed, garlic powder, and mustard seed. Bring to a gentle boil over medium heat, stirring to dissolve the sugar.

Add the jalapeño slices to the syrup. Simmer for 4–5 minutes, stirring occasionally, until slightly softened but still bright.

Use a slotted spoon to pack the jalapeños into sterilized canning jars. Leave ½ inch of headspace. Pour hot syrup over the peppers until covered. Use a butter knife to remove air bubbles.

Wipe the rims with a damp paper towel. Apply lids and rings, tightening just to fingertip tightness.

Place jars in a boiling water bath canner. Process for 15 minutes (adjusting for altitude if needed).

Remove jars and set on a towel or cooling rack. Leave undisturbed for 12–24 hours. Check seals. Label and store in a cool, dark place.