From ChowHound

INGREDIENTS

1 pound Roma tomatoes, cored and halved
1/2 medium white onion, cut into 1/2-inch slices
2 medium garlic cloves, peeled and smashed
1 medium serrano chile, stemmed
1 teaspoon kosher salt, plus more as needed
2 tablespoons coarsely chopped fresh cilantro
1 teaspoon freshly squeezed lime juice, plus more as needed

INSTRUCTIONS

1. Heat the broiler to high and arrange a rack in the upper third of the oven.
2. Place the tomato halves skin-side up on a baking sheet. Scatter the onion, garlic, and serrano around the tomatoes. Broil until the tomato skins start to blacken and blister, about 7 minutes. Transfer the vegetables to a blender, add the measured salt, and blend into a smooth purée. Transfer to a medium heatproof bowl and let cool to room temperature.
3. Stir in the cilantro and lime juice, taste, and season with more salt and lime juice as needed. Store in the refrigerator in a container with a tightfitting lid for up to 4 days.

Roasted Tomato Salsa from AllRecipes

12 roma (plum) tomatoes
2 cloves garlic, unpeeled
1 small onion, quartered
1 jalapeno chile pepper
1 1/2 tablespoons olive oil
1 teaspoon ground cumin
1/4 teaspoon salt
3 tablespoons fresh lime juice
1/4 cup chopped fresh cilantro

Directions

1. Preheat the broiler.
2. In a medium baking dish, place roma (plum) tomatoes, garlic, onion and jalapeno chile pepper. Drizzle with olive oil.
3. Checking often, broil 5 to 10 minutes, or until outsides of vegetables are charred.
4. Remove vegetables from heat. Remove and discard tomato cores, jalapeno stem and garlic skins.
5. In a food processor, coarsely chop the charred vegetables.
6. Transfer to a medium bowl and mix in cumin, salt, lime juice and cilantro.