Preheat oven to 350 degrees F. Arrange cascabel chilies on a sheet pan and toast them in the oven for approximately 3 to 4 minutes. Remove from oven and remove and discard stems and seeds. Place them in a bowl. Cover with boiling water and allow chilies to rehydrate. Remove chilies from water (reserving water), put into a blender and puree with a little of reserved water. Set aside. Raise oven heat to Broil Arrange halved tomatoes and tomatillos cut side down on another sheet pan and place under broiler until skins blacken. Turn them once to heat evenly. Reserve. In a hot grill pan or cast iron skillet, grill red onion slices and garlic until marked and softer. Reserve. To a saucepan over medium hot heat add cascabel puree, tomatoes, tomatillos, red onion, garlic, chipotle puree, Mexican oregano, salt and pepper. Bring mixture to a boil. In a blender, blend mixture until desired consistency. Check seasoning.
Recipe courtesy of Stuart Tarabour, Kitchen Market, New York City, NY