Husk & rinse tomatillos, cutting each into 4-6 pieces, depending on size.
Char jalapenos on open flame (gas cooktop or grill) or under broiler. Cool. Remove stems & seeds and discard.
Peel & rough chop (or smash) garlic cloves. Rough chop onion.
Add all 6 ingredients to a dutch oven. Bring to a boil over medium high heat, then reduce to a simmer, cooking for 20 minutes.
Blend cooked ingredients with immersion/stick blender.
If canning, ladle hot salsa into jars, leaving 1/4-inch headspace. Adjust two-piece caps. Process 15 minutes in a boiling-water canner.
If freezing, cool completely. Portion into small containers (with lids), or freeze in silicone ice trays for cubes of salsa for soups or chili. (Store cubes in freezer bag.)