Prepare the Crust: Start by crushing graham crackers and mixing them with melted butter. Press the mixture firmly into a pie dish, then bake in a preheated oven at 350°F (175°C) for about 10 minutes. Allow it to cool completely.

Make the Filling: In a saucepan, combine granulated sugar and cornstarch with water. Gently stir in freshly squeezed lemon juice and zest, then cook on medium heat until the mixture thickens, roughly 5 minutes.

Temper Egg Yolks: Gradually mix a small amount of the hot filling into the egg yolks to temper them. This step helps prevent scrambling. Once smooth, return this mixture to the saucepan and cook until it reaches a pudding-like consistency.

Finish the Filling: Stir in the unsalted butter into the thickened filling until it’s fully melted and smooth.

Assemble the Pie: Carefully pour the warm filling into the cooled graham cracker crust. Cover and refrigerate for at least 4 hours, or ideally, overnight, allowing it to set perfectly.

Whip Cream Topping: Just before serving, beat the heavy cream until soft peaks form. Gently spread it over the chilled lemon filling.