Pour the cream and milk into a medium saucepan and bring to the boil. Remove from the heat, whisk in the horseradish and wasabi, then cover and leave to stand for 10 minutes. Strain the cream mixture through a chinois and season to taste with salt.
Whisk the gellan into the cream, bring to the boil and cook out for 30 seconds. Pour into a container and place over iced water to set.