1) Cut the salmon in half width-ways and place half the fish skin side down in a deep dish.
2) Wash and shake the dill dry and place it on the fish.
3) Combine the salt, sugar, crushed peppercorns and fennel seeds in a small bowl and sprinkle it evenly over the piece of fish.
4) Place the other half of salmon over the dill, skin side up. Cover the dish with aluminium foil. Place a smaller dish on top of the foil and weigh it with some heavy tins. Refrigerate the salmon for at least 2 and up to 3 days, turning it every 12 hours and basting it with the liquid that collects.
5) Lay each piece of salmon flat on a cutting board, remove the bunch of dill, and sprinkle the top with chopped dill.
6) With a long thin slicing knife, slice the salmon in long thin slices as you would for smoked salmon.
7) Serve with dark pumpernickel bread and mustard sauce. You can also serve with chopped red onion and capers, if desired.
For the mustard sauce:
1) Combine the mustards, sugar and vinegar in a small bowl. Slowly whisk in the oil and stir in the chopped dill. Serve with the gravlax.