Shepherds Pie Potato Bowls

Name: Shepherd's Pie Potato Bowls
Ingredients: 4 large russet potatoes (about 3 pounds); 4 tablespoons unsalted butter plus 1 tablespoon melted butter; 1/4 cup whole milk; 1/4 cup sour cream; Kosher salt and freshly ground black pepper; 1/4 cup chopped fresh chives; 1 small carrot, chopped; 12 ounces ground beef chuck; 2 tablespoons Worcestershire sauce; 1 tablespoon tomato paste; 1 teaspoon fresh thyme leaves; 1/3 cup frozen peas, thawed