2 small yellow onions, cut into wedges
6 garlic cloves, peeled
3 Serrano chili peppers, stemmed (use less for a milder salsa)
1/4 cup vegetable oil
2 teaspoons salt
1 teaspoon cumin
1/4 cup cilantro leaves
1 tablespoon fresh lime juice, from one lime, plus more if needed
Preheat the broiler and set an oven rack about 5 inches beneath the heating element. Line a rimmed baking sheet with aluminum foil. Place the tomatoes, onions, garlic, whole Serrano chile peppers and vegetable oil directly on the prepared baking sheet and toss with your hands. Broil until softened and charred, 10-15 minutes. Transfer the vegetables and juices to a food processor fitted with the metal blade. (If you are concerned about the spice level, add only one Serrano pepper at this point. You can always blend in the others to taste.) Add the salt and cumin and pulse until just slightly chunky. (If you left out some of the Serrano peppers, now's the time to taste and add more.) Add the cilantro and fresh lime juice, and pulse until the cilantro is chopped. Taste and adjust the seasoning with salt and more lime juice if necessary. Be sure to add enough salt and lime to bring out all the flavors. Transfer to bowl and serve warm, at room temperature or slightly chilled. Note: This recipe is not meant for canning.