For the crust: Combine graham cracker crumbs, sugar, and butter in a bowl. Press into a 9-inch pie pan. Bake for 10 minutes. Cool completely.
For the filling: beat the egg yolks and sugar on high in the bowl of an electric mixer with a paddle attachment for 5 minutes, until thick. Add condensed milk, lime zest, and lime juice. Pour into the pie shell and freeze.
For the whipped cream topping: beat the heavy cream on high speed in the bowl of an electric mixer fitted with the whisk attachment until soft peaks form. Add the sugar and vanilla and beat until firm. Spoon or pipe decoratively onto the pie and decorate with lime. Freeze for several hours or overnight.
Notes
Katie’s tips:*I use regular lime if I can’t find keylimes. Keylime are more intense in flavor and smaller than limes.*This recipe I have been making for years. It originates from Ina Garten’s recipe