Remove the backbone and other bones from the salmon and cut in half lengthwise.
Combine the salt, sugar and pepper and rub over the insides of the fish.
Place one piece, skin side down, in a large bowl or serving dish.
Place the dill over the salmon. Top with the other piece of fish, skin side up.
Place a heavy platter over the salmon and weight it down.
Refrigerate, covered, for 24 hours. Turn the fish once or twice during this time.
When finished, remove the salmon from the dish and scrape off the seasonings and dill.
Cut off skin and slice the salmon diagonally into thin slices.
For Gravlaxsas: Combine the mustard, sugar and vinegar in a bowl and mix well together to make a paste. Slowly add the oil, beating well after each addition. Beat until the sauce is the consistency of mayonnaise. Season with salt and pepper and add the dill. Makes 1/2 cup.