First, preheat your oven to 350°F (175°C). Then, combine the graham cracker crumbs, sugar, and melted butter in a bowl and press the mixture into a 9-inch pie dish.

Next, whisk together the sweetened condensed milk, key lime juice, and lime zest in a separate bowl. Pour this filling into the prepared crust and bake for 15-20 minutes, or until the edges are set.

Finally, let the pie cool completely, then chill it in the refrigerator for at least 2 hours before serving. Garnish with whipped cream and fresh lime slices.