Prepare the Crust: In a mixing bowl, combine the graham cracker crumbs, granulated sugar, and melted butter until evenly mixed. Press this mixture into the bottom of a greased baking pan (preferably 9x9 inches) to form the crust. Bake at 350°F (175°C) for about 10 minutes or until lightly golden.
Make the Filling: In another bowl, whisk together the key lime juice, sweetened condensed milk, and eggs until well combined. If you want an extra flavor kick, mix in lime zest.
Combine and Bake: Pour the filling over the baked crust and return the pan to the oven. Bake for an additional 15-20 minutes, or until the filling is set but slightly jiggly.
Cool and Chill: Once baked, allow the bars to cool at room temperature for a bit before transferring them to the refrigerator. Chill for at least 2 hours, or until fully set.
Slice and Serve: Cut into bars and serve with your favorite toppings!