Step 1

Preheat broiler. Place tomatoes, cut side up, on a rimmed baking sheet and sprinkle evenly with 1 teaspoon salt. Add jalapeño, garlic, and onion to baking sheet. Place baking sheet in broiler and cook until tomatoes, jalapeños, garlic, and onion have slightly blackened, about 20 minutes, flipping jalapeño and garlic half way through. Remove from broiler and let sit until cool enough to handle, about 10 minutes.

Step 2

Stem and seed jalapeño and peel garlic. Transfer tomatoes, jalapeño, garlic, and onion to the work bowl of a food processor fitted with a steel blade. Pulse until mixture is finely chopped.

Step 3

Transfer to a medium bowl. Stir in cilantro and lime juice. Season with salt and sugar to taste. Let rest in refrigerator for at least 30 minutes before serving. Store in an airtight container up to a week.