Preheat a lightly-oiled heavy frying pan to medium high heat. A cast iron skillet works best, but any heavy frying pan will do.
Blacken the tomatoes. Place the roma tomato slices into the frying pan and let them fry for approximately 3 minutes without disturbing the slices. Then flip and fry for another 1 to 2 minutes.
Remove the tomatoes from the pan, and place the cascabel peppers in the skillet, cut side down. Fry the peppers for 2 to 3 seconds, then remove quickly. You don't want them to burn.
Place all ingredients into a food processor or blender and pulse blend for approximately 10 seconds, until the salsa reaches a coarsely smooth texture. Add salt, to taste.
Serve immediately, or for the best flavors, refrigerate the salsa for 4 to 6 hours to allow the flavors to fully combine.