In a bowl combine flour, salt sugar, cut in shortening until crumbly. Combine eggs and vinegar, sprinkle over crumb mixture. Gradually add water, tossing with fork until ball forms. Cover and chill for 1 hour or until easy to handle.
On a lightly floured surface, roll out pastry to fit 9 inch pie plate. Trim to 1/2 inch beyond edge of pie plate, flute edges. Place rhubarb in the crust. Whisk the sugar, flour, salt, egg yolks, and cream, pour over the rhubarb. Bake at 350 degrees for 50 - 60 minutes or until knife comes our of center clean.
In a small saucepan, combine 4 tsp of sugar and cornstarch. Gradually add water. Bring to a boil, stirring constantly, cook for 1-2 minutes until thickened. Cool to room temperature. In a small mixing bowl, beat egg whites and cream of tartar until frothy. Add cornstarch mixture, beat in remaining sugar, 1 TBSP at a time, on high until stiff glossy peaks form.
Spread evenly over hour filling, sealing edges of crust. Bake for 15 minutes or until meringue is golden brown. Cool on wire rack for 1 hour. Store in refrigerator.