Preheat broiler on high and position rack approximately 8 to 10 inches beneath heating element.
Place 1 ½ pounds tomatillos, 1 medium jalapeño pepper, 1 medium poblano pepper, half of one medium white onion, and 1 roma tomato on baking sheet, spreading ingredients out across pan so each can roast evenly.
Place baking sheet under preheated broiler. Broil, turning all ingredients over occasionally, until tomatillos, jalapeño, and poblano are blistered and charred on all sides.
Remove baking sheet from broiler and set aside to cool slightly.
Once cooled enough to handle, pull stem out of poblano pepper and discard. Remove seeds and ribs from poblano and discard. Repeat with jalapeño pepper if desired.
Place roasted tomatillos, jalapeño, poblano, onion, and tomato in bowl of food processor. Add 2 cloves garlic, ¼ cup chopped fresh cilantro, 1 ½ teaspoons white vinegar, and ½ teaspoon salt, then secure lid on food processor.
Pulse ingredients in food processor until all ingredients are mostly uniform in size. Taste salsa and add more cilantro and/or salt if desired.
Continue pulsing salsa until desired texture is achieved, then transfer salsa to serving bowl and serve immediately. Alternately, transfer salsa to airtight container and refrigerate until ready to serve.