Peel the mango and cut into very small pieces. Put in a saucepan and pour mango juice so that the pieces are almost covered. Now simmer until the mango pieces are soft, let cool down lukewarm and then they can be mashed. Now add the preserving sugar, a splash of lemon juice and the Havana Club and bring to the boil. Let simmer for 5 minutes while stirring constantly. Pour hot into a glass, close tightly and turn upside down until it is lukewarm. Let it steep overnight.