Source: Delicious & Dependable Slow Cooker Recipes

1/4 cup all-purpose flour
1 (4- to 5-pound) beef brisket, trimmed
1 (1 1/2 ounce) package dry onion soup mix
1/2 teaspoon cracked black peppercorns
1 (10 ounce) can condensed tomato soup
1/4 cup beef stock or water
2 tablespoons packed brown sugar
2 tablespoons balsamic or red wine vinegar
Additional all-purpose flour (optional; see note below)

Rub flour into brisket on both sides and place in crockpot.

In a bowl, combine onion soup mix, peppercorns, tomato soup and beef stock. Pour mixture over brisket. Cover and cook on LOW for 12 hours or on HIGH for 6 hours, until beef is very tender. Transfer brisket to deep platter and slice thinly. Stir brown sugar and vinegar into sauce. Pour over sliced meat or pass separately in a sauceboat.

NOTE: If you prefer a thicker gravy, keep cooked brisket warm and pour sauce into a saucepan. Place 2 tablespoons all-purpose flour in a small bowl. Add 1/4 cup hot cooking liquid, 2 tablespoons at a time, stirring to thoroughly blend after each addition. Stir mixture into remaining sauce and cook, stirring, over medium heat until thickened. Pour over brisket and serve.

Makes 8 to 10 servings.