1/4  Cup Onions -- chopped
    1/4  Cup Celery -- chopped
    1/4  Cup Bell peppers -- chopped
    2 Tablespoons Unsalted butter
    1 Teaspoon Salt
    1 Teaspoon White pepper
    3/4 Teaspoon Black pepper
    3/4 Teaspoon Minced garlic
    1/2 Teaspoon Dry mustard
    1/2 Teaspoon Ground cayenne
    4 Pounds Boneless sirloin roast

Directions:

    In a small bowl combine the onions, celery, bell peppers, butter and
 seasonings, mix well. Place roast in a large roasting pan, fat side up.
 With a large knife make 6 to 12 deep slits in the meat (to form pockets) down
 to a depth of about 1/2 inch from the bottom; do not cut all the way through.
 Fill the pockets to their depths with the vegetable mixture, reserving about 1
 tablespoon of the vegetables to rub over the top of the roast. Bake uncovered
 at 300F until a meat thermometer reads about 160F for medium doneness, about 3 hours. For rarer roast, cook until thermometer reads 140F. Serve immediately, topped with some of the pan drippings if you like.
    From Paul Prudhomme's Louisiana Kitchen