Preheat the oven to 350°F (175°C).

In a mixing bowl, combine graham cracker crumbs, sugar, and melted butter.

Press the mixture firmly into the bottom of a greased 9-inch square baking pan.

Bake for 10 minutes, then remove from the oven and let cool slightly.

In a separate bowl, whisk together the eggs, sweetened condensed milk, key lime juice, lime zest, and sugar until smooth.

Pour the filling over the cooled crust.

Bake for an additional 15 minutes, or until the filling is set.

Allow to cool completely, then refrigerate for at least 2 hours before cutting into bars.