Gently melt the butter, sugar and milk in a pan. Remove from the heat and stir in the condensed milk. Bring the mixture back to the boil for 10 minutes, stirring constantly. Then add the vanilla and continue to heat for a further 10 minutes, now beating constantly with the wooden spoon.
Add the gin, then remove from the heat and continue to beat, by hand for 8 to 10 minutes or with an e