Step 1

Wearing rubber or latex gloves, trim tops off chiles. Working in batches, pulse chiles, bell peppers, and onion in a food processor until chopped into fine bits, about 1 minute per batch. Transfer to a nonreactive 3-quart pot.

Step 2

Stir sugar, vinegar, and salt into chile mixture and bring to a boil over high heat. Reduce heat to medium and simmer, stirring more frequently toward end of cooking to prevent scorching, until thickened, 20 to 30 minutes.

Step 3

Pour or ladle relish into clean, wide-mouth, half-pint jars, leaving 1/2 inch headspace. Wipe rims clean with a damp paper towel. Let cool to room temperature, about 1 hour.

Step 4

Apply clean lids. Enjoy immediately, store in fridge 2 to 3 weeks, or freeze up to 6 months.