Hussarde Sauce

Fry in a saucepan two ounces of lean ham with two ounces of butter, adding two ounces of onions, two cut-up, blanched celery roots, all cut in squares, moisten with half a pint of broth (No. 194a) and half a pint of white wine; add a bunch of parsley garnished with a bay leaf and as much thyme, a clove of garlic and a pinch of tarragon; let the whole boil for half an hour, and then thicken it with two ounces of butter kneaded with one ounce of flour, squeeze in the juice of a lemon, strain the sauce through a tammy and mingle in with it two ounces of grated fresh horseradish.