Combine egg yolks and 1 cup water in top of double boiler.
Add 1/4 cup sugar; mix well.
Cook and stir over boiling water until mixture coats spoon, stirring constantly.
Remove from heat, add gelatin; stir until dissolved.
Add 1/2 cup cold water, the lemon juice, and grenadine.
Chill until thickened.
Prepare whipped topping mix as directed on package.
Beat egg whites and salt until foamy throughout.
Add 1/4 cup sugar, 2 tablespoons at a time, beating thoroughly after each addition.
Continue beating until mixture will form soft, rounded peaks.
Fold into gelatin mixture.
Fold in 1 cup of the prepared whipped topping.
Chill again, if necessary, until mixture will mound.
Spoon into pie shell.
Chill until firm about 4 hours.
Garnish with remaining prepared whipped topping and chocolate curls, if desired.