Shepherds Pie

Name: Shepherds Pie
Ingredients: 2 medium potatoes, cubed; 1/2 cup milk; 4 tablespoons butter, separated; 1 pound ground beef; 1 medium onion, 1/4-inch dice; 1 medium carrot, 1/4-inch dice; 1 medium celery stalk, sliced; 1/2 pound mushroom, sliced; 2/3 cup frozen peas; 2 tablespoons fresh parsley, chopped; 1 teaspoon dried thyme; 1 teaspoon Worcestershire sauce; 1/8 teaspoon nutmeg; 1 cup brown gravy; Salt and pepper