Preheat your oven to 325°F. In a medium bowl, mix the graham cracker crumbs and 1/3 cup sugar. Stir in the melted butter until the crumbs are evenly moistened and the mixture holds together when pressed. Firmly press this mixture into the bottom and about 1 inch up the sides of a 9-inch springform pan to form an even crust.
In a large bowl, beat the softened cream cheese and 1 cup sugar with an electric mixer on medium speed until completely smooth and creamy, about 2-3 minutes. Beat in the eggs one at a time, just until each is incorporated, then mix in the vanilla extract. Be careful not to overmix after adding the eggs.
Pour the cream cheese filling into the prepared crust and spread it into an even layer. Bake for 45-50 minutes, or until the edges are set but the center still has a slight jiggle when the pan is gently shaken. Remove the cheesecake from the oven and let it cool on a wire rack for 10 minutes. Leave the oven on.
Carefully spread the lemon curd in an even layer over the top of the warm cheesecake. In a very clean, grease-free bowl, use an electric mixer with a whisk attachment to beat the egg whites and cream of tartar on medium-high speed until soft peaks form. Gradually add the 1/2 cup sugar, a tablespoon at a time, and continue beating until stiff, glossy peaks form.
Spoon the meringue over the lemon curd layer, spreading it to the edges and creating decorative peaks with the back of your spoon. Bake for 10-12 minutes, or just until the meringue is lightly golden brown. Let the cheesecake cool completely on a wire rack, then refrigerate for at least 4 hours or overnight before serving.