Place brisket, garlic, onion, celery, peppercorns, allspice and bay leaf in a large soup pot. Cover with water.
Simmer covered 3 to 3 1/2 hours until tender, adding water as necessary.
Remove brisket and place in a roasting pan with 1/2 cup of the cooking liquid.
Combine brown sugar and prepared mustard. Salt and pepper brisket and spread with the mustard glaze.
Bake for 15 to 20 minutes at 350° F until glaze bubbles and is browned.
Servings: 6