Preheat your oven to 350°F (175°C). In a medium bowl, mix together the graham cracker crumbs, sugar, and melted butter until well combined. Press this mixture firmly into the bottom and up the sides of a 9-inch pie pan.

Pop the crust into the preheated oven and bake for about 10 minutes until slightly golden.

In a separate bowl, whisk together the sweetened condensed milk, lemon juice, egg yolks, and lemon zest until smooth and creamy. Pour the lemon mixture into the baked crust, spreading it evenly.

Return the pie to the oven and bake for another 15 minutes.

While the pie cools, use an electric mixer to beat the egg whites and cream of tartar together in a clean bowl until soft peaks form.

Gradually add the sugar, continuing to beat until the mixture is glossy and forms stiff peaks. Stir in the vanilla extract.

Spread the meringue over the cooled lemon filling, making sure to seal it well at the edges.

Bake the assembled pie in the oven for an additional 10 minutes or until the meringue is lightly browned.

Allow the pie to cool at room temperature, then refrigerate it for at least 2 hours before serving.