Position rack in center of oven and preheat the oven to 350 degrees F.

In a medium bowl, mix together the graham cracker crumbs, sugar, and melted butter until mixture resembles wet sand. Using your hands, firmly press the mixture across the bottom and up the sides of a 9-inch pie pan. Bake until the crust is golden brown and firm, about 15 minutes. Remove the crust from the oven and transfer to a wire rack to cool completely before filling.

Combine the cream cheese, condensed milk, lemon juice, 3 tablespoons of the lemon zest, and vanilla in a large bowl. Mix on medium speed until smooth. Pour into the cooled pie crust. Refrigerate overnight.

When ready to serve, place the heavy cream, remaining 1/2 tablespoon of lemon zest, and confectioners' sugar in a chilled mixing bowl and whip until stiff peaks form. Top each slice of pie with a dollop of the whipped cream and garnish with fresh berries, if desired.