Carefully wash and peel the salsify, cut into bite-sized pieces and immediately place in a bowl with cold water and a little lemon juice.
Heat oil in a saucepan and add the onions and some of the parsley. Add the black salsify, salt and sweat for 5 minutes. Dust with the flour and let it take on some color, then deglaze with the stock and simmer for 15 minutes on a low heat. Finally, whisk the egg yolks with approx. 2 tablespoons of stock and the juice of half a lemon and add to the ragout. Don`t cook anymore! Season with salt and pepper and serve garnished with parsley.