Combine the graham cracker crumbs, granulated sugar, and salt in a medium bowl. Pour in the melted butter and stir until all crumbs are evenly moistened and the mixture holds together when pressed.

Press the crumb mixture firmly and evenly into the bottom and up the sides of the prepared 9-inch pie dish (use the bottom of a measuring cup for firm, even pressing). Aim for an even 1/4- to 1/2-inch thickness on the bottom and slightly higher up the sides.

Bake the crust in the preheated oven 8–10 minutes, until set and golden at the edges. Remove from oven and let cool slightly while preparing the filling. Reduce oven temperature to 325°F (165°C) if baking the filled pie; otherwise allow to cool completely if making a no-bake chilled pie.

Key Lime Filling

In a medium bowl, whisk together the sweetened condensed milk and lime zest until smooth.

Add the fresh key lime juice and whisk until fully incorporated; the mixture will begin to thicken and take on a pale green color.

Lightly whisk the egg yolks in a separate small bowl until slightly frothy. Temper the yolks by whisking a spoonful of the lime-milk mixture into the yolks, then gradually whisk the yolks back into the main filling bowl until homogeneous. This step ensures a smooth filling and helps stabilize the yolks.

Stir in the pinch of salt. Pour the filling into the warm (or cooled) pre-baked crust, smoothing the top with a spatula.

Bake the filled pie at 325°F (165°C) for 12–15 minutes until the center is just barely set — it should still have a slight wobble. Do not overbake; the filling will continue to set while cooling.

Remove the pie from the oven and let cool to room temperature on a wire rack, about 1 hour. Then refrigerate uncovered for at least 3 hours, preferably overnight, to fully chill and firm the filling.

Whipped Cream Topping (optional)

About 10–20 minutes before serving, chill a mixing bowl and whisk or beaters in the freezer for 5 minutes to help cream whip up better.

Pour the heavy cream, powdered sugar, and vanilla into the chilled bowl. Whip by hand or with an electric mixer on medium-high speed until soft to medium peaks form (takes 2–4 minutes). Do not overbeat or it will become grainy.

Spread or pipe the whipped cream over the chilled pie just before serving. Keep any extra whipped cream refrigerated.

Garnish & Serve

Garnish the pie with thin lime slices and an extra sprinkle of lime zest. Slice with a sharp knife dipped in hot water and wiped dry between cuts for clean slices.

Serve chilled. Store leftovers covered in the refrigerator for up to 3 days.