Perch, German Style

Scale and clean two moderately large perch and put them in a stewpan. Finely
mince the red part of two carrots, some roots of parsley and celery, put them in the
stewpan with the fish, with a bunch of parsley, one onion and a little salt, cover the
perch with white wine and let them boil over a moderate fire for twenty minutes.
Take the fish out when cooked, drain and place them on a hot dish. Take the bunch
of parsley and onions out of the stewpan, then put in with the vegetables some finely
minced raw mushrooms, and cook them for five minutes ; then stir in a piece of
butter kneaded with flour to thicken it ; take the stewpan off the fire, put in some
more butter, cut in small pieces, but not kneaded, add the strained juice of two
lemons, pour it over the fish and serve.