Preheat the broiler. Put the quartered tomatoes, sliced onion, and whole garlic cloves onto a roasting tray, spreading out evenly. Drizzle with plenty of olive oil and season well with salt and pepper and sprinkle with cilantro sprigs. Broil until everything is nicely charred, about 10 minutes (you want lots of deep rich color so don't be afraid if some of the edges get pretty black).
Have sterilized pint jars and lids and screw caps ready (they should all be washed in very hot water). Use a canning funnel and ladle hot salsa into jars, leaving a ½-inch head space. Wipe rims clean with a damp cloth and carefully place lid on and screw cap in place. Process in a boiling water bath for 15 minutes, then place upright on counter for 24 hours (see recipe notes for link to USDA Canning Guidelines). You will hear popping sounds as the jars seal. If after 24 hours, any haven't sealed, put in refrigerator to use now.
Live and learn Mexican cooks. It ain’t a perfect world. The color varies with different chilies. Not using dried guajillo’s it’s gonna be pink. You can thicken it with torn corn tortillas or meal then place in a blender and puree to thicken (NOTE – do not add hot ingredients into a blender – it will blow hot liquid everywhere from the released steam – don’t ask how I know this). You can change the taste using your imagination. Dried chilies are almost always bitter.
Salsas verde and roja are staple Mexican sauces, used daily by the average family. Salsa verde, or green sauce, is typically made with cooked tomatillos, jalapeños, white onions, cilantro, and sometimes lime to taste. Salsa verde can be served warm or cold and can range in spiciness from very mild to completely mouth-searing. Salsa roja, or red sauce, is usually used as a condiment and made with tomatoes, chili peppers, onion, garlic, and fresh cilantro. Both are frequently used as a dip for tortilla chips or served with tacos, grilled meats, and even fish.
Me? I like to kick things up a notch and use a slur of different chilies for the specific qualities that they provide. Four to be exact: Ancho chili for its depth of flavor and subtle earthy notes, Guajillo for its sweetness and notes of raisins and dried fruit, Chile de Arbol for a bit of a kick and a sprinkle of chipotle powder for added smokiness and a little more heat.
Combine ingredients in a large saucepan. Bring to a boil, then reduce heat and simmer, stirring frequently until thick (about 1 hour). Ladle hot mixture into pint jars, leaving 1/2-inch headspace. Adjust lids and process in boiling-water canner for 15 minutes at 0–1,000 feet elevation, 20 minutes at 1,001–6,000 feet, and 25 minutes above 6,000 feet.
UPDATE: Since many of you have asked about a weight measure for the 10 cups of tomatoes, as I've been canning the salsa the last few days, I've done a little experimenting/research. Basically, I've found it varies GREATLY depending on variety. When I used SIX pounds of garden tomatoes + Roma (the paste tomatoes probably only made up about 1/3 of the total), after taking the skins off, lightly crushing, and draining, the yield of tomatoes to use in this recipe was about 2 1/2 cups. When I used TWO pounds of only Roma/paste tomatoes, after taking the skins off, lightly crushing, and draining, the yield of tomatoes to use was a little over one cup. I tend to err on the side of over draining the tomatoes, if anything, so that makes a difference as well. For me, because I usually use paste tomatoes in this recipe, I would plan on around 18-20 pounds (give or take) of Roma/paste tomatoes to get the 10 cups for this recipe...and even more if using tomatoes with a higher water/lower flesh content.
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.
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.