Peel the horseradish root and put it through a juicer: this should yield about 25 ml (1 fl oz) of juice. In a bowl, combine the crème fraîche and cream with a pinch of salt. Mix in the horseradish juice. If your horseradish is not particularly strong, you can gradually mix in more juice to taste. The cream should have a strong flavour but not be too overpowering.