10 fresh plum tomatoes (shucked and cooked in a small amount of water until tender)
1 onion (finely chopped)
2 or more chiles serrano, chopped
1 clove garlic, finely chopped
1 cup cilantro leaves, finely chopped
salt and freshly ground pepper to taste
Combine all ingredients in blender or food processor. Blend until smooth. Taste for seasoning.