Process. Load the graham crackers, butter, and sugar into a food processor and process on high until you achieve fine crumbs.
Press. Grease a pie dish with butter and then press the graham cracker mixture into the bottom and up the sides of the pan.
Chill. Pop the crust in the fridge while you make the filling.
Make the filling
Make the base. In a medium-sized saucepan set over medium heat, whisk together the sugar and cornstarch. Gradually pour in the milk followed by the lemon juice, whisking as you go. Continue to whisk and cook until the filling starts to thicken. Turn the heat to low.
Temper in the eggs. In a small mixing bowl, whisk together the egg yolks until smooth. Add ½ cup of the hot milk mixture to the egg yolks and whisk until combined. Repeat twice. Pour the egg yolk mixture into the filling base, whisking as you go. Continue to cook, whisking consistently, until the filling coats a spoon thickly.
Finish it off. Whisk in the melted butter, lemon zest, and Greek yogurt until smooth. Turn off the heat.
Put it all together. Pour the filling into the chilled pie crust.
Chill. Chill the pie in the fridge for at least 4 hours.
Make the whipped cream. Before serving, combine the heavy cream, powdered sugar, vanilla, and lemon zest in the bowl of a stand mixer. Beat until stiff peaks form.
Decorate. Spread the whipped cream over the lemon filling.
Serve. Serve cold garnished with paper-thin lemon slices.
Notes
Leftover pie should be refrigerated in an airtight container for up to 5 days.