Preheat oven to 400 degrees F.

Remove husks from tomatillos and rinse to remove their natural sticky residue.

Cut the tomatillos in half and place them face-down on a rimmed roasting pan. Add unpeeled garlic cloves to the pan and place in the oven. Roast for 15 to 20 minutes, until they release a goodly amount of liquid and the tops are developing light brown spots.

Remove pan from the oven. Collect the roasted garlic cloves and set aside.

Scrape the tomatillos and their juice into a blender carafe. Peel the garlic cloves and add them to the blender, along with the onions, jalapeño, lime juice, cilantro, salt, and cumin.

Blend at a moderate speed, until the tomatillos are broken down and the other ingredients are just integrated (you should still be able to see small specks of green from the cilantro).

Pour the smooth-ish salsa into a small saucepan and bring to a boil.

When salsa is pipping hot all the way through, pour it into a prepared pint jar (or two half pints, if you prefer).

Wipe rims, apply lids and rings, and process in a boiling water bath canner for 15 minutes at sea level (adjust your processing time if you live at higher elevations).

When time is up, remove jar(s) from canner and set on a folded kitchen towel to cool.

Wait 24 hours and test the seal(s). If the seal(s) are good, jars are shelf stable for up to one year.