A finishing sauce, as opposed to a basting sauce, is used at the end of the cooking process after the temperature has begun to cool in the barbecue pit. If used too early, it will burn/scorch and present a burned bitter taste rather than the sweet/tangy/rich taste you are seeking. This recipes comes from Smoky Hale's "The Great American Barbeque Instruction Book."

Combine the following ingredients in a cooking pot:
    2 (6 ounce) cans Tomotoes - paste or 1
        peck fresh tomatoes stewed, drained and
        reduced to 1 quart
    3 Tablespoons Mustard - dry, heaping,
        (mix in water before adding)
    1 Onion - medium, chopped
    2 cloves Garlic - mashed
    2 cups Water (omit water if using fresh
        tomatoes)
    1 cup vinegar
    1/4 cup Sugar - brown or use turbinado
    1/4 pound Butter - unsalted
    3 tablespoons Paprika - preferably
        Hungaria
    1 teaspoons Cloves - ground or 3 colves
    2 teaspoons Salt - non-iodized
    2 teaspsoons black Pepper - freshly ground
Simmer 1 hour, strain and use or refrigerate. Baste after meat is done and embers temperature is reduced or serve at table.