Cottage Pie

Name: Cottage Pie
Ingredients: 3 tablespoons unsalted butter, melted; 1 large yellow onion, diced medium; 2 large carrots, cut into ¾-inch pieces; Coarse salt and ground pepper; 2 tablespoons tomato paste; 1 pound ground beef or lamb; 2 teaspoons fresh thyme leaves; 1 cup dark (porter) beer; 2 tablespoons all-purpose flour; ¾ cup frozen peas; 1 large russet potato (¾ pound), very thinly sliced