Prepare the Crust: Preheat your oven to 350°F (175°C). In a medium mixing bowl, combine the graham cracker crumbs, melted butter, and granulated sugar. Mix well until all ingredients are thoroughly combined. Press this mixture firmly and evenly into the bottom of a 9x9-inch baking dish to create a solid crust.
Bake the Crust: Place the baking dish in the preheated oven and bake for 10-12 minutes. The crust should become lightly golden. Once baked, remove it from the oven and let it cool for a few minutes.
Make the Filling: In a large mixing bowl, whisk together the sweetened condensed milk, freshly squeezed key lime juice, egg yolks, lime zest, and a pinch of salt. Mix until the filling is smooth and creamy, ensuring no lumps remain.
Combine Layers: Carefully pour the key lime filling over the cooled graham cracker crust. Use a spatula to evenly spread the filling across the whole crust.
Bake the Bars: Return the baking dish to the oven and bake for an additional 15-18 minutes. The filling should be set but will still have a slight jiggle in the center, indicating creaminess.
Cool and Set: Once baked, remove the dish from the oven and allow it to cool at room temperature for about 30 minutes. Then, transfer the dish to the refrigerator and chill for at least 2 hours to completely set.
Slice and Serve: After the bars have chilled, slice them into squares or rectangles using a sharp knife for clean edges.
Optional Topping: For a finishing touch, add a dollop of whipped cream on top of each bar and garnish with a thin slice of key lime if desired.
Notes
Arrange the bars on a decorative platter and sprinkle some extra lime zest around for an appealing presentation!