Char the chiles in a dry skillet.

Char the tomatoes and onion; add the garlic cloves, making sure not to burn them as it can make the salsa bitter.

As each ingredient is charred, transfer it to a blender—start with the chiles, then the garlic, onion, and tomatoes.

Blend and season to taste. Add cilantro and a little hot water at the end, then blend again.

Pour into a container and add a splash of vinegar to help preserve it.