Place tomatoes, jalapenos, onion, and garlic on a lipped tray lined with aluminum foil. Arrange with the larger items on the edges and the smaller items lined down the center. The onion should be cut side down.
Place under broiler on high, and place tray five inches or so below, generally the second shelf down. Broil 10 to 15 minutes total, tending as needed. Roast until vegetables are slightly charred and the skin on the peppers blackened, turning as each side is done and removing each when all sides are charred. Add peppers to a bowl as they are finished, cover, and allow them to steam. Add the tomatillos and onion to another bowl. Cool until easy to handle. Reserve any juices on the sheet tray.
Remove stems from tomatillos and peppers and the seeds from the peppers if desired, working over a bowl to catch the juices. Remove skin and stem from onion and paper from garlic, if using. Add all vegetables to food processor, reserving any juices. Process to desired chunkiness, generally three or four short pulses. Remove to a strainer over the bowl to catch the juices, and set aside the tomatillo mixture.
Place all the juices that have been strained and any juices from the sheet tray or the bowl you’ve worked over and chicken stock in a pan. Heat over medium-high heat and reduce until there is about 1/2 inch of golden syrupy reduction in the bottom of the pan. Watch carefully toward the end, this goes quickly, several minutes at most.
Add the tomatillo mixture to the pan, stir to mix. Add vinegar, salt, and sugar. Add lime if desired. Taste and adjust seasonings.
Keywords: Appetizer, Condiments, Hot Peppers, Jalapeno, Mexican or Southwestern, Salsa, Spreads and Dips, tomatillos, Vinegar