Cream butter well in large mixing bowl. Add 3/4 cup sugar in 2 additions, beating 1 minute after each portion added. Blend in the egg yolks, 1 at a time, beating well after each addition. Beat in the lemon juice and rind; beat in flour and cream.
Beat egg whites on moderately high speed in small deep bowl until frothy. Add cream of tartar; continue beating until soft peaks form. Add remaining 1/4 cup sugar; beat until firm but moist peaks form. Stir in small spoonful of the egg whites into lemon mixture; then fold in remaining egg whites.
Gently, pour filling into baked pie shell. Bake at 400 degrees 10 minutes, reduce oven temperature to 350 degrees and continue baking about 25 minutes or until top is well risen and firm to the touch.
Transfer to cooling rack. Cool completely; then refrigerate 6 hours before serving. Makes one 9" pie.