Easy Shepherd's Pie

Ingredients

• 1 pound ground beef
• 1/2 cup celery, sliced
• 1/3 cup onion
• 1 tablespoon shortening
• salt and pepper to taste
• 1 jar brown gravy
• 1 cup cooked carrots, sliced
• 1/4 teaspoon thyme leaves
• 2 1/2 cups mashed potatoes
• 1/4 cup American cheese, grated