Prep the jalapeños: Wear gloves. Slice jalapeños into ¼-inch rings, discarding stems. Remove seeds for milder flavor (optional).
Make the syrup: In a saucepan, combine sugar, vinegar, water, celery seed, mustard seeds, turmeric, garlic, and salt. Bring to a boil over medium-high heat, stirring until sugar dissolves (3-5 minutes).
Cook the peppers: Add jalapeño slices to the syrup. Simmer on medium heat for 5-7 minutes until peppers soften and darken.
Fill jars: Using a slotted spoon, transfer peppers to sterilized jars, leaving ½-inch headspace. Pour hot syrup over peppers, leaving ¼-inch headspace.
Store: Seal jars and cool to room temperature. Refrigerate for 24 hours before use or can for long-term storage (see canning instructions above).
