Preheat the oven to 350°F (175°C). In a mixing bowl, combine graham cracker crumbs, sugar, and melted butter. Mix until well combined. Press the mixture into the bottom and up the sides of a 9-inch pie pan. Bake for 8-10 minutes until set and lightly golden. Allow to cool.

Prepare the filling

In another bowl, whisk together key lime juice, sweetened condensed milk, egg yolks, and lime zest until smooth. Pour the mixture into the cooled crust.

Bake the pie

Bake the pie for 15-20 minutes until the filling is set but still slightly jiggly in the center. Remove from the oven and let it cool to room temperature, then refrigerate for at least 3 hours before serving.

Making the Buttermilk Chantilly

Whip the cream

In a mixing bowl, combine heavy cream, buttermilk, powdered sugar, and vanilla extract. Whip until soft peaks form. Chill until ready to serve.

Making the Crème Anglaise

Combine ingredients

In a saucepan, combine milk, heavy cream, and sugar. Heat over medium heat until just below boiling.

Temper the egg yolks

In a separate bowl, whisk the egg yolks. Slowly add a small amount of the hot milk mixture into the egg yolks, whisking continuously to temper. Then add the egg yolk mixture back into the saucepan, stirring constantly.

Cook the custard

Cook over low heat, stirring constantly until the mixture thickens enough to coat the back of a spoon. Remove from heat and stir in vanilla. Strain through a fine sieve into a bowl and cool.