4 egg yolks, beaten
1 (14 ounce) can sweetened condensed milk
1/2 cup key lime juice (I only had about 1/3 cup but I think it was even better because the consistence of the tart was just perfect)
1 cup finely ground graham cracker crumbs
2 tbsp sugar
1/4 cup unsalted butter, melted
zest of a few key limes
Preheat oven to 190 degrees C.
Mix graham cracker crumbs, sugar, zest and melted butter. Press mixture into a tart plate. Refrigerate while you make the filling.
Combine the egg yolks, sweetened condensed milk and lime juice. Mix well and pour into unbaked graham cracker shell.
Bake in preheated oven for 15 minutes. Allow to cool and refrigerate for at least one hour or overnight before serving.