Use this rich sauce for dipping or pouring over enchiladas or tostadas. This is a basic recipe that you can add more heat or garlic to depending on your tastes. This makes about 4 cups.
Preheat oven to broil. First, you need to blister the tomatoes and Serrano chiles under a broiler. Place them on a cooking pan, about 4” from the top of the oven. Using tongs, turn often for about 3-4 minutes until tomatoes and chiles are blistered all over. Cut off stems and remove seeds from chiles (unless you want the salsa to be really hot). If you would prefer a less smoky-tasting sauce, the skins can be removed from the chiles and tomatoes. Pulse blistered tomatoes and chiles in a food processor along with the onions and garlic. This mixture can be as smooth or chunky as you prefer. Taste for salt and pepper. Heat a skillet to medium-high. Add blended mixture to the skillet and lower the heat to medium-low. Cook for about 5-8 minutes until bubbly. Serve warm or cold.
To reduce heat in chiles, cut out the membranes and seeds from inside. After handling cut peppers, be certain to wash your hands, knives and cutting boards with soap. Pepper juice burns and can be dangerous if rubbed into eyes.