Mix flour, butter, sugar, and salt until crumbly. Press into a 9 x 13 baking pan. Bake at 350º for 15 min or until crust is golden brown.
Beat egg yolks, sugar, cream, salt, and flour together. With a spoon, fold in Rhubarb until coated. Pour on top of baked crust. Return to oven for another 45 min.
While filling is baking, beat egg whites, sugar and cream of tarter until soft peaks form. Once the filling is finished, pour over baked Rhubarb mixture and bake another 15 min. Let cool to room temperature before serving.
Serve warm or cold