Beat egg yolks to a thick froth. Gradually beat in the sugar, flour, and melted butter or margarine. If using fresh rhubarb, use 3 tablespoons flour; if using frozen rhubarb, only use 2 tablespoons. Stir in rhubarb pieces.
Dump rhubarb mixture into an unbaked, chilled pie shell. Cover filling with top crust. Flute and vent the pie.
Bake on bottom rack of oven at 425 degrees F (220 degrees C) for 10 minutes, then at 375 degrees F (190 degrees C) for 30 minutes. Cool somewhat before cutting.