Weed out any tomatillos brown(ish) in color and so squishy they appear ready-to-explode. They are ready for recycling.
Put the roasted tomatillos into a blender. Make sure to also add the garlic and olive oil liquid left over. Add a chopped jalapeño, 1 teaspoon of fresh lime juice, a pinch of salt, 1/2 cup of chopped onions, and a 1/2 cup of chopped cilantro.
Blend until smooth-ish.
Transfer into a small pot and bring to a low boil, simmering for another 15 minutes.
This is a good time to boil the jars, lids, and bands. If possible, use a funnel made for canning jars. It will keep a lot of your end product inside, not down the sides of the jar.
Extract a jar, fill to within 1/2-1" of the top, apply band and lid. Repeat repeatedly. Label. Wait for the lids to pop, then file away in the pantry.