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. Onion should be cut side down.
Place under broiler on high, five inches or so below, generally the second shelf down. Broil for about 10 to 15 minutes total until vegetables are slightly charred, watching carefully and turning and removing as needed. Cool until easy to handle.
Remove vegetables and reserve any juices on the sheet tray. Over a strainer with a bowl under it, remove seeds and stem from tomatoes. Reserve the juices and add tomatoes to a food processor fitted with a chopping blade. Remove stems, skin, and seeds from the jalapeno and add to the tomatoes. Remove skin and stem from onion and add to the tomatoes. Squeeze garlic from the paper and add to the tomatoes.
Pulse to desired chunkiness, then add juices from the sheet tray, vinegar, salt, and sugar. Taste and adjust as desired.
Depending on how juicy the vegetables are and how much juice was given off in the broiling process, you may wish to add some of the juice that was strained from the tomatoes to the salsa. Go by your personal taste and add until desired consistency is reached.
Notes: