1. In a small bowl, beat the egg yolks and lime zest until the mixture turns light green.2. Beat in condensed milk, and slowly stir in juice. Set aside.
3. Preheat oven to 325 F.
4. In a separate bowl, mix graham cracker crumbs and sugar. Stir in melted butter until well blended.
5. Spoon graham cracker mixture into a 9-inch pie plate and press down along the bottom and sides to create the pie crust.
6. Bake the pie crust for 10-15 minutes or until lightly browned. Remove and let cool.
7. Pour lime filling into the crust, and bake for 15 minutes until the center sets.
8. Remove from oven and cool.
10. Cover and refrigerate for several hours until well-chilled.
11. Garnish with whipped cream and lime slices.