There are probably better recipes than this, but this is pretty easy and usually is pretty good. I never measure amounts, just go by how much I want to make and how hot or not hot I want it.
-In salted water boil tomatoes, half a small onion, some garlic pods, and the peppers or pepper combination of your choice. My go to pepper combination is a jalapeno or two, one serrano, and a couple of dry chile de ancho chili's that you buy at the Mexican grocery and or most grocery stores nowadays. For that pepper amount I would use 3-4 large tomatoes or 6-8 roma tomatoes. I have found I like Roma's better when they are just overripe.
-Boil the above for a while, like simmering for about 15-18 min.
-In a separate pan/pot, mix about a teaspoon full of either Knorr Caldo de Tomate or Knorr Caldo de Pollo with about 6 ounces of water, heat and dissolve the mix.
-After the above stuff has simmered, drain it and put it into a blender. Put in another 2-3 1/4" onion slices, and maybe a small garlic pod and Cilantro leaves to taste. Grind it up in a blender, but do not puree. I go easy on Cilantro because I am not that crazy about it, just like a hint of it.
-Depending on the consistency, add some of the Knorr broth mix. And blend again.
-I season with dried Cumin, a couple of dashes and if I have it some Goya Adobo seasoning. Oh, and also add some lime juice at some point, not too much. I use the broth mix as a salt addition, occasionally I will use some seasoned salt and a couple of squirts of Maggie Sauce.