Sterilize four 8-ounce canning jars and lids (see Disclaimer).
Preheat the broiler. Put the poblano halves skin-side up on a foil-lined broiler pan with the onion and garlic. Broil until the poblano is charred and the onion and garlic are browned, about 8 minutes. Cool the poblano slightly, then peel.
Pulse the tomatillos in a food processor in batches until coarsely chopped, then transfer to a bowl. Add the poblano, onion and garlic to the processor and pulse until coarsely chopped (do not overprocess). Transfer to a large, wide saucepan. Add the cumin, lime juice, vinegar, sugar and 1 tablespoon salt. Bring to a boil over high heat and cook, stirring occasionally, until slightly reduced, 3 to 4 minutes.
Add the tomatillos and jalapenos to the pan, cover and return to a boil. Cook until heated through, 3 to 4 more minutes.
Fill the jars with the tomatillo mixture, leaving 3/4 inch headspace, then seal and process. After opening, top the salsa with cilantro, if desired.
Photograph by Charles Masters
Properly handled sterilized equipment will keep canned foods in good condition for one year. Making sure hands, equipment and surfaces in your canning area are clean is the first step in canning. Tips: Jars should be made from glass and free of any chips or cracks. Preserving or canning jars are topped with glass, plastic or metal lids that have a rubberlike seal. Two-piece metal lids are most common. To prepare jars before filling: Wash jars with hot, soapy water, rinse them well and arrange them open-side up, without touching, on a tray. To sterilize jars, boil them in a large saucepan, covered with water, for 10 minutes. Jars have to be sterilized only if the food to be preserved will be processed for less than 10 minutes in a boiling-water bath or pressure canner. To sterilize jars, boil them in a large saucepan, covered with water, for 10 minutes. Follow manufacturer's instructions for cleaning and preparing lids and bands. Use tongs or jar lifters to remove hot sterilized jars from the boiling water. Be sure the tongs are sterilized too: Dip the tong ends in boiling water for a few minutes before using them. All items used in the process of making jams, jellies, preserves and pickles must be clean, including any towels and especially your hands. After the jars are prepared, you can preserve the food. It is important to follow any canning and processing instructions included in the recipe and refer to USDA guidelines about the sterilization of canned products. Find Information information on canning can be found at the National Center for Home Food Preservation website: http://nchfp.uga.edu/.