– Roughly chop tomatoes, serranos, garlic clove, and onion.
– Place in your blender with ¼ cup of water, and process until smooth (or slightly coarse, if you prefer).
– Heat the oil in a medium-size frying pan over medium-high heat, and pour in the salsa and stir.
– Once the salsa starts boiling, reduce the heat and gently simmer for about 13-15 minutes, stirring from time to time, until all the ingredients are well cooked. If it needs it, add more water; this will depend on how juicy the tomatoes are.
– Once done, season with salt and serve. This sauce will keep well for about 3 days in your refrigerator.