Preheat the oven to 350°F. In a bowl, stir together the graham cracker crumbs, granulated sugar, salt, and melted butter until the crumbs look evenly moistened.
Press the crust mixture firmly into the bottom and up the sides of a 9 inch pie pan. Bake for 8 minutes, then set the crust aside to cool while you make the filling.
In a large bowl, whisk the egg yolks for about 1 minute, until they look slightly thickened. Add the sweetened condensed milk and whisk until smooth.
Whisk in the key lime juice, key lime zest, vanilla extract, and salt until the filling is creamy and fully combined.
Pour the filling into the cooled crust and smooth the top. Bake for 12 to 15 minutes, until the center is just set with a slight jiggle.
Let the pie cool at room temperature for about 30 minutes, then refrigerate for at least 3 hours, or overnight, until fully chilled and set.
To make the whipped cream, beat the heavy whipping cream, powdered sugar, and vanilla extract on medium high speed until stiff peaks form.
Spread or pipe the whipped cream over the chilled pie. Garnish with key lime zest, slice, and serve cold.
