Step 1: Preheat the Oven and Make the Crust.

Preheat the oven to 350°F (175°C).

Combine the graham crackers and granulated sugar in a food processor. Pulse until fine crumbs form.

Pour in the melted butter. Pulse until the crumbs are well coated and stick together when pinched.

Press the mixture into the bottom and up the sides of a 9-inch pie plate.

Bake the crust until just set, about 10 minutes.

Set aside to cool slightly, about 10 minutes.

Step 2: Make the Filling.

Whisk the egg yolks, condensed milk, key lime juice, and lime zest in a medium bowl until combined.

Pour the filling into the partially baked crust.

Step 3: Bake the Pie.

Bake the pie until the center is set but still slightly jiggly, about 15 minutes.

Let cool for 30 minutes.

Then, refrigerate until chilled, at least 1 hour.

Step 4: Make the Whipped Cream and Serve.

Before serving, beat the heavy cream and powdered sugar in a large bowl with a mixer on medium speed until soft peaks form.

Spread the whipped cream on the chilled pie.

Garnish with lime zest.

Slice and serve chilled.