(United States) Serves 4 to 8 (makes about 40 dumplings) INGREDIENTS For the Dough 2 cups unbleached all-purpose flour, plus some extra for dusting 2 tablespoons unsalted butter, melted 1 large egg, beaten ¼ cup warm water 3 tablespoons sour cream ½ teaspoon salt For the Filling 2 medium baking potatoes, such as russet 1…