Prep the tomatillos. Remove husks and rinse off the sticky residue. Pat dry.
Preheat your oven to 425°F (220°C). Line a sheet pan with parchment for easy cleanup.
Roast the vegetables. Add tomatillos, onion quarters, whole chilies, and garlic cloves to the pan. Drizzle with a little oil (optional) and roast 15–20 minutes, flipping once, until tomatillos blister and release juice and peppers soften.
A few charred spots are great for flavor.
Blend to your preferred texture. Transfer roasted vegetables and any pan juices to a blender or food processor. Add cilantro, 2 tablespoons lime juice, 2 tablespoons vinegar, 1 teaspoon salt, and cumin if using. Pulse for chunky, or blend smooth.
Add a splash of water or broth only if too thick.
Taste and adjust. You want bright, tangy, and lightly salty. Add more salt, lime juice, or vinegar to balance. For canning, keep the total acidity (lime + vinegar) at least 3–4 tablespoons for this batch to maintain safe pH.
Simmer for a few minutes. Pour the salsa into a pot and bring to a gentle simmer for 5–10 minutes.
This melds flavors and prepares it for canning. If using fresh now, you can cool and serve.
Prepare for canning. Wash jars, lids, and rings. Keep jars hot (in simmering water or a 200°F oven).
Bring a large canning pot to a boil with a rack on the bottom.
Fill the jars. Ladle hot salsa into hot jars, leaving 1/2-inch headspace. Wipe rims with a damp towel, center lids, and screw on rings to fingertip-tight.
Process in a boiling water bath. Place jars on the rack in the boiling pot. Ensure they’re covered by at least 1 inch of water.
Process 15 minutes for half-pints (adjust for altitude; see Pitfalls section). Start timing when water returns to a rolling boil.
Cool and check seals. Remove jars, let cool 12–24 hours. Lids should be concave and not flex when pressed.
Label and store sealed jars in a cool, dark place. Refrigerate any unsealed jars and use within a week.