1 can (14–16 oz) of peeled, diced tomatoes
1 bunch of fresh cilantro (aka coriander leaf, Mexican parsley)
3–6 fresh serrano chili peppers (the more the spicier; start with 3)
½ fresh finely chopped onion
1 tsp salt
1 pinch of pepper and/or garlic to taste (optional)
Add onion to blender.
Wash and chop the cilantro, removing only the very bottom of the stem. Add to blender.
Wash and chop the chile peppers, then add to blender.
Open the canned tomatoes, add to blender.
Add the salt.
Blend slowly, to thoroughly mix ingredients; do not completely blend.
Serve chilled, with a meal, as a dip for corn tortilla chips, as a garnish, etc.