Tip the cranberries, sugar and rosemary into a pan with about 100ml water. Cook over a low heat for about 15 mins, stirring occasionally, until all the cranberries have burst and the sauce has thickened to a syrupy consistency. Fresh cranberries thicken the sauce more readily than frozen, so it may take a little longer, but be careful not to let the sauce become a jam.

Scoop out the rosemary and stir through the gin. Cook for 1 min more, then leave to cool. Will keep, covered, in the fridge for three days.