Add tomatoes and serranos to pot of water and bring to a boil. Let it boil for one minute and then take off of heat. Leave ingredients in water for about 5 min's. Remove items from water very carefully they will be hot. Remove stem button and skin from tomatoes. Place in blender. Remove stems from peppers and cut in half. At this time you will either want to remove the seeds for a milder sauce or leave the seeds in for a hotter sauce. I leave the seeds in!! Add peppers to blender.
Take your half of a white onion and quarter it. Add to blender. (You can use a yellow onion if you prefer) At this point you will find you might want to adjust the amount of onion to less or more. The onion can overpower the salsa so a med onion with the ends cut off I have found to be just enough.
Wash and add a small handful of cilantro, 1/2 a small garlic clove, stewed tomatoes(un-drained) and teaspoon of salt. (Garlic is another ingredient you can adjust to your taste. Also using a couple dashes of powdered garlic will work just fine.) Cover and run blender on "chop" until ingredients are chopped up completely. At this time you will want to taste before pouring it out of the blender to see if you need a touch of salt or some other ingredient. I have used this recipe for so long it is pretty much set but everyone's tastes can differ. I hope you enjoy this salsa. It is a great appetizer with tortilla chips or add it to ANY food you like especially breakfast eggs!!! It will keep for about 2 to 2 1/2 weeks in your refrigerator. Enjoy!!!