In a small to medium saucepan, add all of the ingredients and cook for 15 minutes over medium heat.
3 Roma tomatoes, ¼ of a large onion, 1 large garlic clove , 2 cups broth, ½ teaspoon each: dried oregano, salt & black pepper , 2 chile guajillos (see substitutes below)
Puree: Add the guajillos to a blender with 1 cup of the cooking liquid. Puree well.
Using a fine strainer, strain the guajillos to remove all of the pulp.
In same blender, add the rest of the vegetables and the remainder of the cooking liquid. Puree well. See note #2
In a medium saucepan, heat 1 tablespoon of oil and add the sauces very carefully & slowly to make sure it doesn't splatter all over the stove!
Cook on low heat for about 10 to 15 minutes until all of the flavors have incorporated well and the sauce thickens up a little bit.
Taste for salt & pepper and add more if needed according to taste.
Drizzle hot over tacos dorados, sopes, gorditas, tostadas, etc.