The key to this recipe is to char the tomatoes and peppers on the stovetop. I tried to do it in the oven once and roast the tomatoes & peppers, bad move. It will take you about 20 minutes, but sooooooo worth the wait. You’ll need to rotate the veggies from time to time, so all the sides are pretty even. Here is what the vegetables will look like once they are done:

When your tomatoes and onion look softened, it’s time to remove them and set aside or place in your blender or food processor along with the garlic. Now add the Arbol peppers to the hot griddle and slightly roast them, this will be a very fast step since the peppers skins burn easily, which gives them an unpleasant bitter taste, so be sure to turn them and roast the peppers without burning them.
Simple, fresh and easy to make. A winning Mexican restaurant style salsa prepared with plum tomatoes, onion cilantro, and serrano peppers. Fresh tomatoes, not canned, star in this recipe. In Mexico, it is known as salsa roja (red sauce) or salsa de mesa (table sauce). And just like in the U.S., it is served in every restaurant before your meal with tortilla chips.
Here is a tasty homemade salsa to accompany your crispy tortilla chips.  Many salsa recipes call for canned tomatoes and chilies (i.e., already cooked).  I find that using fresh ingredients, and then cooking the salsa briefly, yields the best flavor.  It sweetens the tomatoes and brings out their flavor.  (Note, canned tomatoes have also been semi-cooked)  The other purpose cooking it serves is to bring the mixture up to the required temperature for canning.
IMPORTANT: Follow the directions carefully and exactly for each recipe. Use the amounts of each vegetable listed in the recipe. Add the amount of vinegar or lemon juice listed. You may decrease the amount of spices if desired. Do not can salsas that do not follow these or other research-tested recipes. These salsas may be frozen or stored in the refrigerator. Do not thicken salsas with flour or cornstarch before canning. After you open a jar to use, you may pour off some of the liquid or thicken with cornstarch.
In the blender, add bell peppers, onion, assorted peppers, lime juice, cilantro, salt, garlic powder, chili powder, and cumin. Once jalapenos have sat for 10 minutes, remove from zip-lock bag and pinch the skins off. Discard skins and place jalapenos in blender. Blend on medium speed until contents are blended but slightly chunky. Pour contents in pot with tomatoes.

Douglas, I was just wondering about using the iron skillet or comal and the tomatoes. I tried a different recipe the other day and used my iron skillet to toast the ancho chilies, tomatoes and serrano peppers it called for. After blending all the ingredients, I used the same skillet to heat and cook the finished sauce. I only thought about it after the fact and wondered if the acidic sauce changed in flavor by using the iron skillet. I am sure our grandmothers used their iron for everything and never worried about the acid in them, so I am sure this question is moot, but I still want to know. I am not a very good cook, even though I try, and last weeks sauce did not turn out very tasty. I am going to give this one a try and hope it comes out better. Thank you for posting this.
This recipe is a great starting point to develop your own Mexican salsa recipe. Adjust any or all of the ingredients to suit your tastes. Although this recipe calls for charring the chiles, you can also make it without charring them. Add more chiles for a spicier sauce or reduce the number for a milder version. Substituting jalapeño chiles for the serrano chiles will make a milder salsa too.
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