Beef Roast with Au Jus

The recipe is an old family one. I think my sister made this up.  BTW it's very simple and easy to make and really smells delicious while roasting.

1 beef roast, 3-4 pounds
4 tablespoons butter
1 tablespoon Worcestershire Sauce
1 thick slice onion, about 1/2 " thick
coarse salt & fresh pepper
1 can beef broth

1. Put beef roast in roasting pan.
2. Melt the butter and Worcestershire Sauce together in a small saucepan.
3. Pour over the meat.
4. Put the onion on the roast and secure with a toothpick.
5. Salt & pepper.
6. Roast about 25 minutes per pound for medium rare or however you like it.
7. When the roast is finished remove to another pan.
8. Add a little water to the pan and stir.
9. Add 1 can beef broth.
10. Strain the broth mixture.
11. Heat and serve with the beef sandwiches.