In a medium bowl, combine graham cracker crumbs, sugar, and melted butter until it resembles wet sand. Firmly press this mixture into the bottom and up the sides of a 9-inch pie dish. Place the crust in the freezer for about 15 minutes to set.

Using a large mixing bowl, whip the heavy cream on high speed until stiff peaks form, then set aside. In another bowl, blend softened cream cheese and sweetened condensed milk until smooth and creamy. To this, add fresh lemon and key lime zest, vanilla extract, sour cream, and both lemon and key lime juices, mixing until fully incorporated.

Gently fold the whipped cream into the filling mixture using a spatula until there are no visible streaks.

Pour the filling into your chilled crust, smoothing the top with a spatula for an even surface. Place the pie in the refrigerator and chill for at least 2 hours, or until the filling is fully set.

After the pie has chilled, whip any remaining cream to soft peaks and spread it gently on top. Garnish with thin slices of lemon and lime before serving cold.