In a sauce pan at medium heat, bring 4 cups of water to a simmer.

Slice an X on the bottoms of tomatoes. Roughly chop the serrano peppers. Transfer tomatoes, peppers, onion and garlic to simmering water. Cook for 10 minutes.

Remove tomatoes from water and carefully peel skins away and discard skins.

Transfer tomatoes, peppers, onion and garlic to blender jar along with 2 cups of the cooking water from sauce pan. Add bouillon, pepper, oregano and salt tot taste. Blend on high until smooth.

Preheat 1 1/2 tbsp of oil in a sauce pan, at medium heat, for a few minutes. Once hot, pour in the caldillo sauce from the blender jar. Stir well. Cook at a steady simmer for 15-20 minutes. Taste for salt.