Pulverize graham crackers in a food processor, drizzle in butter. Press into pie pan and bake for 5 minutes. Take out of oven and let cool on counter.
Make the filling while the crust is cooling. Separate eggs, saving one egg white in a separate bowl. Whisk the egg yolks and add in the condensed milk and key lime juice.
Using a whisk or hand mixer, whisk the egg white to stiff peaks.
Fold in the lime mixture with the egg white until fully incorporated. Pour into pie crust.
Bake for 15-20 minutes until the pie is slightly jiggly when you take it out of the oven. Place in the fridge and let set up for a minimum of 6 hours. Top with whipped cream or whipped topping.