01 - Preheat oven to 350°F. Have all ingredients measured and ready before beginning.
02 - In a mixing bowl, combine graham cracker crumbs, granulated sugar, and melted butter until the mixture resembles wet sand. Press firmly and evenly into the bottom and up the sides of a 9-inch pie dish.
03 - Bake the crust for 8 to 10 minutes until lightly golden and set. Remove from the oven and allow to cool completely while preparing the filling.
04 - In a medium saucepan, whisk together granulated sugar, cornstarch, all-purpose flour, and salt. Gradually whisk in the water, lemon zest, and lemon juice until smooth and fully combined.
05 - Place the saucepan over medium heat and stir constantly until the mixture thickens and begins to bubble, approximately 4 to 6 minutes.
06 - Slowly whisk a few spoonfuls of the hot lemon mixture into the lightly beaten egg yolks to gradually raise their temperature without scrambling. Pour the tempered egg mixture back into the saucepan while stirring continuously.
07 - Continue cooking and stirring for 2 minutes until the filling is thick and glossy. Remove from heat and stir in the butter until completely melted and smoothly incorporated.
08 - Pour the hot lemon filling into the cooled crust, spreading evenly. Allow the pie to cool to room temperature, then refrigerate for at least 2 hours until the filling is fully set.
09 - Using an electric mixer, beat the heavy whipping cream, powdered sugar, and vanilla extract on medium-high speed until stiff peaks form. Do not overbeat.
10 - Spread or pipe the whipped cream over the thoroughly chilled pie. Slice into 8 even portions and serve chilled.