Place the cherries, sugar and water in the top of a double boiler. Cook over medium heat for about 10 minutes, to allow the fruit to soften. Take out 1/2 cup of the cherries and drain the juices back into the pan. Puree the rest of the cherries. Roughly chop the 1/2 cup of cherries and mix back into the puree. Chill.
Add the half and half and egg to a blender and blend until smooth. Whisk in chilled cherry mixture. Add the heavy cream and vanilla. Blend well. Chill.
Transfer mixture to your ice cream maker and freeze according to manufacturer's instructions.