Preheat your oven to 325°F (163°C).

In a medium mixing bowl, combine graham cracker crumbs, sugar, and melted unsalted butter until evenly moistened. Transfer to a 9-inch springform pan and press firmly to create an even crust. Bake for 10 minutes, then let cool.

In a large bowl, beat softened cream cheese until smooth. Gradually add granulated sugar, then mix in sour cream, eggs, lemon zest, lemon juice, and heavy cream. Mix until silky and smooth.

Pour the filling over the cooled crust and bake in the oven for 55-60 minutes until the edges are set and the center jiggles slightly. Turn off the oven and let the cheesecake cool inside for 1 hour with the door ajar.

Refrigerate for at least 4 hours or ideally overnight to fully set.

In a clean bowl, beat egg whites and cream of tartar until soft peaks form. Gradually add granulated sugar while beating until stiff peaks form. Add warm lemon juice and mix for an additional 30 seconds.

Spread the meringue evenly over the cheesecake and create peaks with a spatula.

Increase oven temperature to 350°F (177°C) and bake the meringue for 8-10 minutes until lightly golden brown. Let cool at room temperature for 1 hour.

Return the cheesecake to the refrigerator for an additional hour to ensure the meringue sets properly before serving.