Boil 8 roma tomatoes with 3 serrano peppers for 10 minutes or so then drain.
Peel tomatoes and remove seeds (they're bitter).
Dice 1/2 large white onion and put in cold water then drain.
Roughly chop 1/4 cup cilantro.
Toss it all in a blender or food processor.
Add salt, pepper, sugar, and an acid like lemon juice or pickle juice.
Blend to desired consistency.