Stir together peppercorns, coriander seeds, salt and sugar. Lay out a large piece of plastic wrap and sprinkle with about one third of the mixture. Lay fish on top, skin side down, then sprinkle with remaining mixture and scatter with dill. Wrap tightly in plastic wrap and place in a shallow baking pan. Place another pan on top and weigh it down with a heavy skillet or a couple of large cans.
Refrigerate for two days, turning fish over about every 12 hours. (There’ll be some seeping juices.) Discard dill and any larger pieces of coriander or pepper and store covered in fresh wrap without weighting. To serve, cut fish from skin in very thin slices.