Skin and clean the fish, removing guts and blood, and rinse them in cold water.
Cut a slice the whole way through each plaice. This is to keep the super fresh fish from contracting and bending too musch in the pan while frying.
Dip the plaices in flur, spices, salt and pepper.
Fry the plaices in a pan for about 3-4 minutes on each side. The longitudinal cut in the fish aids here too: you can spoon some of the melted frying butter over the thick (head) end of the fish and some of the butter will be absorbed. This helpes the thick and thin (tail) end of the fish to get done at the same time without any part drying out.
Scrub the potatoes in cold water and boil them in lightly salted water for 8-10 minutes. Turn off the heat and let the potatoes get done in the hot water for another 5 minutes or so.
Serve the plaice with the potatoes and the butter from the frying pan, freshened up with a dash of vinegar. As a tasty side dish you can add pickled cranberries.