Onion Beef Au Jus

We tried this one from a Taste of Home cookbook. Super good and easy! I used the crock pot.

1 boneless beef rump roast (4 pounds)
2 Tbsp vegetable oil
2 large sweet onions, cut into 1/4 inch slices
6 Tbsp marg, softened, divided
5 cups water
1/2 cup soy sauce
1 envelope onion soup mix
1 garlic clove, minced
1 tsp browning sauce, optional
1 loaf French bread
1 cup shredded Swiss cheese
Brown roast on all sides. Place roast in roasting pan or crock pot. Saute onions in 2 Tbsp butter until tender. Add the water, soy sauce, soup mix, garlic and browning sauce. Pour over roast. Cover and bake at 325 for 2 1/2 hours or crock pot on low for 6 hours. Let stand for 10 minutes before slicing. Return meat to pan juices. Slice bread in half lengthwise; cut into 3 inch slices. Spread remaining butter on bread. Place on a baking sheet. Broil until golden brown. Top with beef and onions; sprinkle with cheese. Broil again 1-2 inches until cheese melted. Serve with pan juices.