Prepare the ingredients by washing the Tomatillos and Jalapenos thoroughly.
Cut the Jalapeno in half, de-seed and de-vein it, and then boil it in a pan for approximately 7 minutes until it is soft. Remove the Jalapeno and place it on a baking sheet.
Place the Tomatillos, Garlic with Peel On, Onion with skin on, and Bellpepper on the same baking sheet next to the Jalapeno.
Turn the oven on broil and place the baking sheet on the middle rack. Cook all the ingredients until they have a nice char, turning the tomatillos over to char on all sides. The tomatillos are done when they are starting to lighten and turn a slight yellow color. Remove each ingredient as it gets done roasting, making sure not to burn the garlic.
In a small bowl, smash the garlic to a paste, then add it to the blender with the rest of the roasted items. Peel the skins off the tomatillos when they are finished charring, then add them to the blender.
Pulse the mixture in the blender until it is thick like a salsa. Add salt, cumin, to taste, and cilantro, then the vinegar, and pulse a few more times. Note that if you prefer a Green Taco Sauce, you can strain the seeds from the tomatillos and omit cilantro.