Crust (if making your own; optionally you can use a 9" pre-made crust):
Preheat oven to 350°F.
Stir crumbs, sugar, and melted butter together with a fork. Press into a 9" pie plate. Bake for 5-7 minutes until slightly browned. Let cool completely before filling.
Place eggs in a medium saucepan and whisk until combined. Whisk in sugar, salt, lime juice, and zest.
Add the diced butter to the pan and turn on the heat to medium. Constantly whisk until the butter melts and the mixture begins to thicken, 5-10 minutes. Don't walk away, keep whisking, and make sure it doesn't boil. Once it thickens, remove it from the heat and pour it into the prepared crust. Let it cool and set completely at room temperature, at least one hour. Refrigerate uncovered until ready to serve. Garnish with lime slices and/or lime zest. Optionally, serve with whipped cream.