Place the oven rack directly underneath the broiler and turn the broiler on high.
Place the tomatoes, jalapeños, and onion on a baking sheet and drizzle with the oil. Rub it all over the vegetables to coat, then place them in the oven and broil for 5-8 minutes, until the skins are blistered and blackened.
Flip the vegetables over, add the garlic to the baking sheet, and broil for 5-8 more minutes, until blackened and blistered.
If you don't want the salsa too spicy, remove and discard the jalapeño seeds. Transfer everything to a food processor or blender. Add the cilantro sprigs, lime juice, and salt. Pulse a few times for a chunky salsa or blend for one minute for a smooth salsa. Taste and season with more salt if needed.
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Notes
Storage. This roasted tomato salsa will keep in an airtight container in the fridge for 5-7 days. To freeze, transfer to a freezer-safe container and freeze for up to 3 months. Thaw overnight in the fridge.