Preheat oven to 375°. On a lightly floured surface, roll pastry dough to a 1/8-in.-thick circle; transfer to a 9-in. pie plate. Trim pastry to 1/2 in. beyond rim of plate; flute edge., Spread cranberries evenly into crust; sprinkle with brown sugar and walnuts. In a bowl, beat egg on high speed until thick and pale yellow, about 5 minutes. Gradually beat in sugar. Beat in flour and melted butter (mixture will be thick). Spoon over cranberries, spreading evenly., Bake on a lower oven rack until crust is golden brown, 40-45 minutes. Cover pie loosely with foil during the last 10-15 minutes if needed to prevent overbrowning. Remove foil. Cool on a wire rack. Serve warm with ice cream.