How to Make It
Preheat a charcoal grill to medium-high (400°F to 450°F). Grill whole tomatoes, uncovered, turning often, until evenly blackened, 6 to 7 minutes.
Grill onion, serrano chile, and jalapeño, uncovered, turning often, until blackened, about 5 minutes.
Place grilled vegetables, garlic, and vinegar in a food processor, and pulse until chopped and combined. Sprinkle with salt.