Make the crust by combining the graham cracker crumbs with melted butter and sugar in a small bowl. Press the crust mixture into an 8-inch pie pan.
Prepare the cream cheese filling by mixing cream cheese with 1/4 cup sugar, vanilla and an egg using an electric mixer. Mix well until smooth. Pour cream cheese filling into graham cracker crust and bake for 30 to 35 minutes or until center is cooked. A knife stuck in the middle of the filling should come out mostly clean.
As the pie cools, make the lemon filling by combining sugar with cornstarch, salt and water in a small saucepan. Set mixture over low heat and bring to a simmer, stirring often.
Whisk in egg yolks, then add lemon juice and butter. When mixture simmers again remove it immediately from the heat.
Pour the lemon filling over the cream cheese filling, and let the pie cool. When cool, chill pie in the refrigerator for several hours before serving.