01 - Set broiler or grill to high heat to prepare for roasting the vegetables.
02 - Place tomatoes cut side down, onion quarters, jalapeños, and unpeeled garlic cloves on a foil-lined baking sheet.
03 - Broil or grill for 10 to 12 minutes, turning once halfway through; remove garlic after 8 minutes to prevent burning.
04 - Allow vegetables to cool slightly, then peel the garlic cloves.
05 - Transfer charred tomatoes, onion, jalapeños, peeled garlic, cilantro, lime juice, salt, cumin (if using), and black pepper to a food processor or blender.
06 - Pulse until reaching desired texture, either chunky or smooth; adjust seasoning as preferred.
07 - Transfer salsa to a bowl, cover, and refrigerate for at least 30 minutes to develop flavors. Serve chilled with tortilla chips or as a topping.