Preheat your oven to 350°F and prepare a 9-inch glass pie plate by spraying it with cooking spray. If you don’t have a glass pie plate, you can use two tin foil disposable pie pans. Keep in mind that you will need two since they tend to be shallower than a traditional pie plate, affecting the final structure of your pie.
In a medium bowl, combine the crushed graham crackers with the melted butter. Use a fork to mix these ingredients until they are well combined. The mixture should resemble wet sand, holding together when pressed. This will form the base of your pie.
Transfer the crumb mixture into the prepared pie plate. Press it firmly into the bottom and up the sides, ensuring an even layer. This step is crucial for a sturdy crust that holds the filling well. Once you’re satisfied with the crust, pop it into the oven and bake for 10 minutes, until it’s slightly golden.
While the crust is baking, you can prepare the filling. In a large bowl, add the sweetened condensed milk, egg yolks, and whisk them together until smooth. It’s essential to blend these ingredients thoroughly to incorporate air, which will help achieve a light filling.
Next, add the freshly squeezed Key lime juice to the mixture. Whisk again until everything is combined well. The acidity from the lime juice will react with the condensed milk and yolks, creating a luscious filling.
Once your crust is done baking, remove it from the oven and let it cool slightly. Pour the lime filling into the pre-baked crust. Spread it evenly with a spatula, ensuring the filling reaches all edges.
For the meringue, pour the egg whites into a bowl of a stand mixer fitted with a whisk attachment (or use a large bowl and electric hand mixer). Be careful not to get any yolk in the whites, as this will prevent them from whipping properly. Add the cream of tartar and vanilla extract, and beat the mixture on high speed until soft peaks form. This step is crucial, as it will give your meringue that fluffy texture.
Gradually add the granulated sugar while continuing to beat on high until you achieve stiff peaks. You should be able to turn the bowl upside down without the meringue falling out. This indicates the sugar has fully dissolved and the meringue is ready for the pie.
Spread the meringue evenly over the top of the lime filling, making sure to seal the edges well. This prevents the meringue from shrinking away from the filling. Create peaks in the meringue for an aesthetically pleasing look. Bake the pie for about 15 minutes if using a glass pie plate, or 10 to 15 minutes if using disposable pans until the meringue is lightly browned.
Remove the pie from the oven and let it cool at room temperature on a wire rack before transferring it to the fridge. Chilling is highly recommended for at least 2 hours; this will enhance the flavor and texture of the pie, making it easier to slice when serving.
