Prepare the crust: In a bowl, mix together the graham cracker crumbs, sugar, and melted butter until well combined. Press the mixture into the bottom and up the sides of a 9-inch pie dish to form the crust. Use the back of a spoon to pack it tightly. Refrigerate the crust while you prepare the filling.

1. Make the pudding filling: In a large mixing bowl, whisk together the instant lemon pudding mix and cold milk for about 2 minutes until it thickens. Stir in the vanilla extract and set aside.
2. Make the whipped cream: In a separate bowl, use a hand mixer to beat the heavy whipping cream and powdered sugar on high until soft peaks form. This should take about 3-4 minutes.
3. Combine the pudding and whipped cream: Gently fold the whipped cream into the lemon pudding mixture until well combined and smooth.
4. Assemble the pie: Pour the lemon pudding mixture into the prepared graham cracker crust, smoothing the top with a spatula.
5. Chill: Refrigerate the pie for at least 4 hours, or until it is set and firm to the touch.
6. Serve: Once the pie is set, garnish with fresh lemon slices if desired, and serve chilled.