Salsa De Tomate Verde (Cooked Tomatillo Sauce)

1 lb tomatillos, husks removed
4 jalapenos or serranos
2 TBS roughly chopped cilantro
1 garlic clove, peeled and chopped
1 small onion, chopped
1 1/2 TBS oil
salt to taste

Put tomatillos and chiles into a pan and cover with water. Simmer 10 minutes. Add 1/3 cup reserved cooking liquid, chiles, cilantro, onion, and garlic to the blender. Add tomatillos and blend 10 seconds. Heat oil in pan and add sauce. Cook 8 minutes until thickened. Add salt to taste.