Soak the gelatine in ice-cold water for 10 minutes. Bring the milk and cream up to the boil. Take off the heat and whisk in the gelatine. Season with the horseradish, salt and vinegar to your liking – the vinegar helps bring out the flavour of the horseradish. Pass through a chinoise into a clean tub and leave to set at room temperature before placing in the fridge until needed.