Put half a cup of rum in a saucepan and heat on medium heat util boiling. Let it simmer for a couple minutes to boil off some of the alcohol an concentrate the rum flavours. Leave it to chill.
Whisk together the egg, egg yolk, sugar and maple syrup until well mixed.
Whisk in the double cream.
Whisk in the rum and the chilled concentrated rum.
Whisk in enough milk to reach the target volume (about half a litre of milk)
Transfer to the freezer and crank!