Shepherd's Pie is a traditional English dish, made with lamb or mutton. Americans typically make Shepherd's Pie with beef.
The English (and Australians and New Zealanders) call the beef dish a 'Cottage pie'. Naming conventions aside, Shepherd's Pie is essentially a casserole, lined with cooked meat and vegetables, topped with mashed potatoes, and baked.
Here is a basic recipe for a simple ground beef Shepherd's Pie.

Ingredients
1 lbs ground round Lamb (or beef foir cottage pie)
1 onion chopped
1-2 cups vegetables - chopped carrots, corn, peas
1 ½ - 2 lbs potatoes (3 big ones)
8 tablespoons butter (1 stick)
½ cup beef broth
1 teaspoon Worcestershire sauce
Salt, pepper, other seasonings of choice

Preparation
1. Peel and quarter potatoes, boil in salted water until tender (about 20 minutes).
2. While the potatoes are cooking, melt 4 Tablespoons butter (½ a stick) in large frying pan.
3. Sauté onions in butter until tender over medium heat (10 mins). If you are adding vegetables, add them according to cooking time. Put any carrots in with the onions. Add corn or peas either at the end of the cooking of the onions, or after the meat has initially cooked.

4. Add ground beef and sauté until no longer pink. Add salt and pepper. Add worcesterchire sauce. Add half a cup of beef broth and cook, uncovered, over low heat for 10 minutes, adding more beef broth as necessary to keep moist.
5. Mash potatoes in bowl with remainder of butter, season to taste.

6. Place beef and onions in baking dish. Distribute mashed potatoes on top. Rough up with a fork so that there are peaks that will brown nicely. You can use the fork to make some designs in the potatoes as well.
7. Cook in 400 degree oven until bubbling and brown (about 30 minutes). Broil for last few minutes if necessary to brown.
Serves four.
Source: Simply Recipes
I'd like to thank the lady who's recipe I used here - Aparently she's going to sue me for putting her recipe on this site. Even though I credited the source, Elise is having a hissy fit. I'd therefore like to strongly recommend that you don't use the above recipe and ignore this post. Or use the recipe, but add some thyme or marjoram which, my legal staff tells me, enables you to avoid any legal ramifications. If you cook a Shepherd's Pie using the recipe above, there's a good chance the mind police will come over to your house and rob you of all your ideas.
I apologise to Elise while at the same time disparing of the narrow mindedness of it all. I don't run this site for money - obviously she thinks of hers as a business - I do this because I enjoy food and feel that its worthwhile sharing that enjoyment