Slice the crosnes across in 1cm thick slices. Heat the butter in a pot over medium heat, when the foam subsides, add the diced shallot. Cook stirring regularly until translucent and add a pinch of salt and grinding of black pepper, then add the sliced crones.
Lower the heat and cook gently for about 5 to 7 minutes and add the cognac; cook for a further 3 to 4 minutes until most of the alcohol has evaporated. Add the chicken stock, lower the heat to minimum and cook uncovered for about 30 to 40 minutes until reduced by one third. Taste for seasoning and add the cream, cook for a further 10 minutes. Finish off with a light pinch of hot cayenne or paprika. Serve in hot bowls with some crusty bread, or garnish with fresh chopped chives. Bright red currants will also be a great finishing touch.