Sift flour and sugar together, add egg, beat thoroughly and add rhubarb. Line piepan with pastry and pour in filling. Cover with top crust and bake in a very hot oven (425F) for 10 minutes. Reduce temperature to mocedart (350F) and bake 35 minutes longer. Variations: Arrange pastry strips into lattice design over the top instead of using top crust. Omit top crust, cool slightly and cover with whipped cream.