For meringue, in a large bowl, beat the egg whites, vinegar, vanilla and 1/8 teaspoon salt on medium speed until soft peaks form. Gradually beat in 1 cup sugar, 1 tablespoon at a time, on high until stiff glossy peaks form and sugar is dissolved. , Line baking sheet with parchment. Spoon egg white mixture into 8 mounds on paper. Shape into cups with a spoon. , Bake at 300° for 35 minutes. Turn oven off and leave door closed; let shells dry in oven at least 1 hour. Remove shells from paper. When thoroughly cooled, store in an airtight container. , For custard, in a small saucepan, combine the cornstarch and remaining sugar and salt. Stir in water until smooth. Cook and stir over medium-high heat until thickened and bubbly. Reduce heat; cook and stir 2 minutes longer. Remove from the heat., Beat egg yolks. Stir a small amount of hot mixture into egg yolks; return all to pan, stirring constantly. Bring to a gentle boil; cook and stir 2 minutes longer. Remove from the heat; gently stir in the lemon juice, zest and butter. Cool to room temperature without stirring. Chill. , Just before serving, fill meringue shells with custard and top with whipped cream.