Preheat oven to 450*. Fit pie crust firmly into bottom and up side of a 9 inch tart pan with removable bottom. Bake until light golden, 9-11 minutes. Remove from oven. Reduce oven temperature to 350*.
Combine water, 2 tablespoons sugar and cornstarch in a small saucepan; mix well. Cook over medium-high heat, stirring constantly, until mixture becomes clear, 2-3 minutes. Remove from heat; set aside.
Combine egg whites, cream of tartar and salt in a large bowl. Beat with an electric mixer at medium-high speed until frothy. Add remaining sugar gradually to egg whites; beating until soft peaks form and being careful not to let egg whites become dry, 2-3 minutes. Reduce speed to medium; gradually add cornstarch mixture, one spoonful at a time. Increase speed to high; beat until meringue is smooth and satiny, about 2 minutes.
Spoon apple pie filling into baked crust. Spoon meringue into a pastry bag fitted with a large star tip. Pipe meringue on top of pie filling. Bake until meringue is golden, 12-15 minutes. Cool tart completely on a wire rack. Loosen crust from side of pan; remove side. Cut into wedges to serve.