1medium-size white onioncut into 1/2-inch thick slices
1/2cupchopped fresh cilantro
1/3cupfresh lime juiceabout 4 limes
Preheat grill to medium high. Place tomatoes and peppers on grill whole. Allow to skin to char, 8–10 minutes. Flip tomatoes and peppers and allow other side to char, about 5 minutes longer.
Remove tomatoes and peppers from grill. Place in bowl and cover with tin foil (this helps soften the skins).
Preheat oven to 425. Arrange onions and garlic on a rimmed baking sheet lined with tin foil. Bake for 20 minutes. Remove garlic. Bake onions another 20 minutes or until starting to brown (alternatively, you can grill onions . . . my grill was filled with tomatoes and peppers because I made a double batch and I didn't want to grill the garlic).
Meanwhile, remove skins from tomatoes, and coarsely chop. Coarsely chop onion. Mince garlic. Place tomato, onion, garlic, salt, and sugar in a medium stainless steel or enameled saucepan.
Peel peppers; remove and discard seeds, if desired. Finely chop peppers; add to tomato mixture. Bring to a boil, stirring often. Reduce heat, and simmer 2 minutes. Stir in cilantro and lime juice.
Ladle hot salsa into hot jars, leaving 1⁄2-inch headspace. Remove air bubbles. Wipe jar rims. Center lids on jars. Apply bands fingertip-tight. Place jars in boiling water canner.
Process jars 20 minutes, adjusting for altitude. Turn off heat; remove lid and let jars stand 5 minutes. Remove jars and cool.
Source: Butcher, Meredith L., Ed. The All New Ball Book of Canning and Preserving. New York: Oxmoor House. 2016. Page 176.