Peel the celeriac, chop into cubes and cook in boiling water with the juice of the lemon. Purée the cooked celeriac in a processor, add 100 g butter and season. Peel and mince the shallot.
Bring the wine to the boil, add the shallots, allow to reduce by half, add the crème de cassis and the blackcurrants and reduce again. The sauce should be syrupy. Whis