Shepherds Pie

Name: Shepherd's Pie
Ingredients: 2 tablespoons unsalted butter; 1 small onion, finely chopped; 1 rib celery, finely chopped; 2 medium carrots, cut into 1/2-inch pieces; 1 teaspoon chopped fresh thyme; 2 pounds ground beef chuck; Kosher salt and freshly ground black pepper; 2 tablespoons tomato paste; 2 tablespoons all-purpose flour; 2 cups beef stock; 2 tablespoons Worcestershire sauce; 2 tablespoons chopped flat-leaf parsley; 1 cup frozen peas, not thawed; 2 pounds russet potatoes (about 2 large), peeled and halved; Kosher salt; 1/3 cup heavy cream; 1 stick unsalted butter; 1 cup shredded sharp orange cheddar cheese