Preheat the oven to 350°F.
Make the piecrust. In a medium-size mixing bowl, combine the graham cracker crumbs and melted butter, mixing to blend.
Put 1/4 cup of the mixture into each of eight 4-inch individual fluted tartlet pans with removable bottoms. Using your fingers, press the crust into the bottom and up the sides of the pans. Put them on a baking sheet and bake for 15 minutes. Remove from the oven and let cool completely on a wire rack.
Make the filling. In a medium-size saucepan, combine the sugar and cornstarch and whisk until blended. In a small mixing bowl, combine the lemon juice and water. Slowly whisk this into the sugar-and-cornstarch mixture. Over medium heat, bring to a gentle boil and whisk occasionally until the mixture begins to thicken, about 5 minutes.
Add 1/4 cup of the hot mixture to the beaten egg yolks and whisk to blend. Add this mixture to the saucepan and whisk until thick enough to coat the back of a wooden spoon, about 5 minutes.
Pour about 1/3 cup of the mixture into each of the tart shells. Place them on a baking sheet and refrigerate until the filling sets, about 2 hours. Carefully remove the tarts from the pans and place on a baking sheet.
Make the meringue. Preheat the oven to 450°F.
Combine the egg whites and sugar in a large mixing bowl and beat on high speed with an electric mixer until stiff peaks form. Spread the top of each tart with an equal portion of the meringue. Bake on the top rack of the oven until the meringue is lightly brown, about 6 minutes. Let cool before serving.
Yield: 8 tarts