The main ingredient is red tomato, known as "jitomate" in Mexico. This is a basic recipe and there are many variations.
- Roast tomatoes and allow to cool to room temperature.
- Place roasted tomatoes, garlic, and chili in the mortar and grind to a paste with the pestle.
- Add onion, if using, and salt. Mix.
Let the salsa stand for a better flavor.
If you don't have mortar and pestle, use a blender or food processor.