1. Preheat the oven to 425°F. Roll out the pastry and place in a 9-inch glass pie plate with fluted edges. Prick the bottom and sides with a fork. Bake for 10-12 minutes or until golden brown. Remove crust from the oven and reduce heat to 350°F.
2. Place 1 1/2 cups sugar and 3 egg yolks in the bowl fitted with the mixer. Mix at speed 6 for 1 minute. Add the cornstarch, water, butter and lemon juice. Launch the dessert program at speed 5 at 190°F for 12 minutes, without the stopper. Increase the emperature to 210°F and mix another 2 minutes. Pour filling into the baked pie shell.
3. Wash the Prep&Cook bowl. Add egg whites, cream of tartar and remaining 1/4 cup sugar in the bowl fitted with the whisk. Launch at speed 8 for 5 minutes or until stiff, without the stopper. Spread over the filling, sealing the edges.
4. Bake at 350°F for 12-15 minutes or until meringue is golden brown. Cool for 3 hours before serving.