Preheat broiler to high. Line a large baking sheet with aluminum foil for easy cleanup.
Place the tomatoes, onion halves, jalapenos and garlic on the baking sheet. Drizzle with olive oil and rub it all over the vegetables to coat.
Place the baking sheet in oven and broil for 10-15 minutes, flipping the vegetables halfway through, until the skins have blistered and blackened.
Carefully remove and discard the stems of the jalapeños. If you don't want the salsa too spicy, you can also remove and discard the seeds.
Transfer everything to a food processor or blender and 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.
Video
Notes
Have a gas stove or a grill? Instead of using the broiler, you can also carefully roast the vegetables directly over the burner or grill grates until blackened and blistered.
Storage - This salsa can be stored in an airtight container in the fridge for up to 1 week.