Combine all the ingredients in a blender and process until smooth.
If you have an ice cream machine, you can put it in there and follow the instructions. If, like me, you don't have one, you can simply freeze it in a freezer-safe container. Give it a stir 4-5 times while it is freezing. It can keep for many months in the freezer.
Use honeydew from your own garden, or buy honeydew in season. I freeze lemon juice from my lemon trees to use in this.