Make the graham cracker crust: In a medium bowl, mix together the graham cracker crumbs, sugar, salt, and butter until well combined. Press the mixture evenly against the bottom and sides of an 8-inch pie dish.
3. Step
Bake the crust until it begins to turn golden brown, about 8 minutes. Remove from the oven and let cool completely.
4. Step
Make the Key lime filing: In a large bowl, mix together the egg yolks, sweetened condensed milk, lime zest, and lime juice with an electric hand mixer on medium-high speed until smooth and frothy, about 2 minutes.
5. Step
Pour the filling into the cooled pie crust.
6. Step
Bake the pie until the filling is mostly set with a gentle wiggle in the center, about 20 minutes. Do not let the filling brown. Let the pie cool at room temperature for at least 30 minutes, then transfer to the refrigerator and chill until ready to serve.
7. Step
Make the topping: In a medium bowl, use a whisk or electric hand mixer to whip the heavy cream and powdered sugar until stiff peaks form.
8. Step
Top the chilled pie with the whipped cream and Key lime zest and slices.
