Sheperds pie recipes are usually made with ground beef, mashed potatoes, mixed vegetables, diced tomatoes and cheddar cheese.

You need about 120 servings for 100 people.
Here is the basic proportions for 6 servings:

1 pound ground beef
1/2 pound (1 large) yellow onion, chopped
1/2 pound (8-10 oz.) can diced tomatoes, drained
Salt and pepper
1 pound mixed vegetable, frozen or canned, drain if canned
1 1/2 pound (4 med.) potatoes, cooked and mashed
1/4 pound (1 cup) cheddar cheese, grated
grated Parmesan cheese to dust the pan.

Preheat oven to 350 degrees. Grease your casserole and dust with grated Parmesan cheese.

Make your mashed potatoes by your favorite recipe. I like my freezable holdable mashed potato recipe in the big pots section.

In a frying pan or skillet, brown ground beef. Remove from pan and brown the onions. Drain any excess fat from the ground beef.

Combine the diced tomatoes, salt, pepper, mixed vegetables and ground beef mixture. Place in the dish.

Top with mashed potatoes and shredded cheddar cheese.