Mix all but the first 3 ingredients (meat cooking bag, flour) in a medium saucepan. Heat to blend flavors, bring only to boiling. Cool.
Put flour in baking bag; add meat and cooled basting sauce. Seal bag, bake in 350 degree oven until internal temperature of 185 degrees (about 1 1/2 hours).
For a non-alcoholic version substitute one or more bottles of Italian salad dressing.
Remove meat from bag; pour sauce into pan; thicken with flour while heating gently. Serve as a gravy.