Preparation of the Crust

1. Gather Ingredients: Start by having all your crust ingredients ready: graham cracker crumbs, sugar (typically granulated), and melted butter.
2. Combine: In a medium bowl, mix the graham cracker crumbs, sugar, and melted butter until the mixture resembles wet sand.
3. Press into Pie Dish: Evenly press the crumb mixture into the bottom and up the sides of a 9-inch pie dish. Use the bottom of a glass or measuring cup to create a compact, smooth crust.
4. Pre-bake (Optional): For a slightly crispier crust, pre-bake it in a preheated oven at 375 degrees F (190 degrees C) for about 8-10 minutes. Let cool before adding the filling.

Making the Filling

1. Gather Ingredients: Assemble your filling ingredients: egg yolks, sweetened condensed milk, and Key lime juice. Zest your Key limes before juicing to make the most of their flavor.
2. Whisk Egg Yolks and Zest: In a large bowl, whisk the egg yolks and lime zest together for about a minute or two, until combined and slightly thickened.
3. Incorporate Condensed Milk: Slowly whisk the sweetened condensed milk into the egg yolk mixture until fully incorporated.
4. Add Key Lime Juice: Gradually whisk in the Key lime juice. The filling will thicken slightly as you mix.

Baking and Cooling

1. Preheat Oven: Make sure your oven is preheated to 375 degrees F (190 degrees C).
2. Pour Filling: Carefully pour the prepared filling into the prepared graham cracker crust.
3. Bake: Place the pie on a baking sheet and bake for 15-18 minutes, or until the filling is just set. The center might jiggle slightly, but it will firm up as it cools.
4. Cool Completely: Allow the pie to cool to room temperature on a wire rack. This could take 1-2 hours.
5. Refrigerate: After cooling, refrigerate the pie for at least 4 hours, or ideally overnight. Chilling solidifies the filling and allows the flavors to meld perfectly.