Step 1Place half the fish, skin side down, in a deep glass dish. Spread the dill over the fish. Sprinkle the salt, sugar and peppercorns over the dill. Top with the other half of the fish, skin side up.
Step 2Cover with aluminum foil or lightly with plastic wrap and weight with a board and a 5-pound weight. Refrigerate for 48 to 72 hours, turning the salmon and basting every 12 hours with accumulated juices.
Step 3To serve, remove the fish from the marinade, scrape away the dill and spices, and pat dry. Slice the salmon thinly on the diagonal and serve on small plates or squares of pumpernickel. Garnish with lemon wedges and black pepper and accompany with dill mustard sauce.
Step 1Mix together the mustard, sour cream and dill. Cover and refrigerate until ready to use. The sauce will keep for up to 3 days if refrigerated. Yields 2 cups.