1 cup key lime juice (more or less to taste)
1 cup water
1/4 cup vodka (optional)
1/4 cup vanilla sugar (more or less to taste)
1/2 cup heavy cream
To make vanilla sugar, stir together white sugar and a used vanilla bean with a fork or clean hands. The texture of the sugar rubs the last black specks from the inside of the vanilla pod. Waste not, want not.