Combine the rock salt, 75g sugar, and crushed white peppercorns in a bowl.
Stir in half of the chopped dill.
Line a large shallow dish with cling film.
Spread a quarter of the curing mix in the dish and place one salmon fillet on top, skin side down.
Spread half of the remaining mixture over the fish and top with the second fillet, skin side up.
Apply the last of the mixture to the top and wrap the salmon tightly in cling film.
Weight the salmon down in the fridge for 2 to 3 days, turning it every 6 hours.
Unwrap the salmon, rinse off the cure with cold water, and pat dry with paper towels.
Place one fillet on fresh cling film, cover with the remaining dill, top with the second fillet, and chill for 6 hours.
Whisk mustard, 1 tbsp sugar, vinegar, and egg yolk in a bowl to make the sauce.
Gradually whisk in the oil until the sauce reaches a thick, smooth consistency.
Stir in 1 tbsp chopped dill and season with salt and pepper.
Carve the salmon into thin slices without the skin.
Plate several slices per person with a spoonful of mustard sauce.
Serve immediately with rye bread.