Let egg whites stand at room temperature for 30 minutes. Divide the chilled tart pastry into 4 portions. On a lightly floured surface, roll each potion to 1/8-inch thickness. Cut into a 5-1/2-inch round. Fit rounds into 4 ungreased 4-inch tart pans with removable bottoms. (Or, roll pastry to an 11-inch round; fit pastry into a 9-inch tart pan with removable bottom.) Line pastry in pan(s) with a double thickness of foil. Place on a baking sheet.
Bake in a 350 degree F oven for 15 minutes; remove foil. Bake for 5 to 6 minutes more for small tarts (12 to 15 minutes for large tart) or until golden. Cool in pan(s) on a wire rack.
For filling, in a saucepan combine 1/2 cup of the sugar, fruit puree, and butter. Bring just to boiling over medium heat, stirring occasionally. Beat the 3 egg slightly with a fork. Slowly add fruit mixture, beating continuously. Return to saucepan; heat and stir over medium heat 4 to 5 minutes until slightly thickened (do not boil). Strain; cover. Keep warm.
For meringue, in a large mixing bowl combine the egg whites, vanilla, and cream of tartar. Beat with an electric mixer on high speed until soft peaks form (tips curl). Gradually add the remaining sugar, beating on high speed until stiff peaks form (tips stand straight).
To assemble, remove pastry shell(s) from pan(s). Place shell(s) on a baking sheet. Spoon fruit filling into shells. Spoon meringue into a pastry bag fitted with a large star tip. Pipe meringue onto the top of tart(s) in a woven pattern. Bake in a 350 degree F oven for 10 to 12 minutes for small tarts (15 minutes for large tart) or until meringue edges are golden. Cool 30 minutes on a wire rack. Chill in the refrigerator for 3 to 6 hours. Makes 4 small tarts or 1 large tart.
Sweet Tart Pastry
In a medium mixing bowl stir together all-purpose flour and sugar. Using a pastry blender, cut in butter until pieces are pea-size. In a small mixing bowl stir together egg yolks and water. Gradually stir egg yolk mixture into dry mixture. Using your fingers, gently knead dough just until a ball forms. If necessary, cover with plastic wrap and chill in refrigerator for 30 to 60 minutes or until dough is easy to handle.