To make the crust, crush crackers in a food processor or zip-top bag. Pour them into a bowl and stir in sugar and melted butter. Press into a pie pan—I also love using a nonstick springform pan. Bake for 5 minutes or until golden and set, and remove from oven.
To make the filling, whisk lime zest, lime juice, and egg yolks in a mixing bowl. Add condensed milk and mix on high until smooth and thick. Pour mixture into crust and bake for 15 minutes.
Pour filling into crust and bake in middle of oven 15 minutes. Cool pie completely on rack (filling will set as it cools), then chill, covered, for at least an hour but hopefully longer!!! (Eight hours is ideal!)
Serve with sweetened whipped cream and more grated lime zest OR do what I did and make a topping you can cover the whole pie with, a sort of buttercream frosting, if you will.
To make the frosting: Just before serving, cream the butter in a bowl with an electric mixer then add lime zest, vanilla extract, salt, powdered sugar, and milk—and decorate the heck out of your pie. I love using flowers to decorate because it's super simple but so pretty and colorful. :)