Preheat the oven to 375°F (190°C).

In a medium bowl, combine the graham cracker crumbs, granulated sugar, and melted butter. Press the mixture into the bottom and up the sides of a 9-inch (23 cm) pie dish.

Bake the crust for 12 minutes, or until golden brown. Remove from the oven and let cool completely.

In a large bowl, whisk together the egg yolks, sweetened condensed milk, key lime juice, and key lime zest until well combined.

Pour the key lime mixture into the cooled pie crust. Smooth the top with a spatula.

Place the pie in the refrigerator and chill for at least 4 hours, or until set.

In a medium bowl, whip the heavy cream and confectioners' sugar until soft peaks form.

Spread the whipped cream over the chilled pie.

Garnish with thinly sliced lime before serving.

Slice and serve chilled.