Heat the milk in a saucepan to a simmer. Put the lemon zest and vanilla bean in a bowl, and add the hot milk. When cool, cover and allow to infuse for about 8 hours or overnight in the refrigerator.

In a saucepan, add the zest from the 2 lemons and 2 limes, lemon juice, lime juice, sugar, and 2 cups water. Stir and bring to a boil. Simmer for 2 to 3 minutes until the sugar dissolves. Strain and ...