Make a pie crust: In a bowl, combine flour, salt and sugar; cut in shortening until crumbly. Combine egg and vinegar; sprinkle over crumb mixture. Gradually add water, tossing with a fork until a ball forms. Cover and chill for 1 hour or until easy to handle.
On a lightly floured surface, roll out pastry to fit a 9-in. pie plate. Trim to 1/2 inches beyond edge of plate; flute edges.
Place rhubarb in crust. Whisk the sugar, flour, salt, egg yolks and cream; pour over rhubarb. Bake at 350° for 50-60 minutes or until a knife comes out clean.
In a small saucepan, combine 4 teaspoons sugar and cornstarch. Gradually stir in water. Bring to a boil, stirring constantly; cook for 1-2 minutes or until thickened. Cool to room temperature.
In a small bowl, beat egg whites and cream of tartar until frothy. Add cornstarch mixture; beat on high until soft peaks form. Gradually beat in remaining sugar, 1 tablespoon at a time, on high until stiff glossy peaks form and sugar is dissolved.
Spread evenly over hot filling, sealing edges to crust. Bake for 15 minutes or until meringue is golden brown. Cool on a wire rack for 1 hour. Store in the refrigerator. Yield: 6-8 servings.
Note: If using frozen rhubarb, measure rhubarb while still frozen, then thaw completely. Drain in a colander, but do not press liquid out.