(Shepherd's Roast with Drunken Sauce] ) In Hidalgo, halves of mutton are hung over a wood fire and slowly turned until the meat is cooked and the outside is crisp and black. Toward the end of the cooking process, the roast is basted with lightly salted butter. It's served with Salsa Borracha, below. FOR THE ROAST: Use a 5-pound leg of lamb and roast it on a spit over a charcoal fire until done the way you like it ( 1.5 to 2 hours). Baste from time to time with lightly salted butter in which a clove of garlic has been crushed and a pinch of dry mustard added. In an ungreased skillet, cook the dried chili pasillas for a few minutes, turning occasionally to prevent burning. Skip this step if chili powder is used. Remove stems and seeds and cover them with the water, saving the skins. In about 0.75 hour, put the chilies in a blender with the remaining ingredients and 4 tablespoons of the water in which the chili seeds were soaked. Blend all until smooth. Strain the remaining chile water and add to sauce. Serve, either by pouring a little over each portion of meat, or letting guests help themselves. Add more chili powder or chilies for a hotter sauce. Makes 6 servings. From "The Art of Mexican Cooking" by Jan Aaron and Sachs Salom. Doubleday and Company, N.Y., 1965.