Mix together the kosher salt, sugar, and peppercorns. Rub each side of the salmon thoroughly with the salt and sugar mixture and place them in a deep dish, on top of each other, with the dill in between. Wrap with plastic wrap and set aside at room temperature for about 1 to 2 hours.
Place in the refrigerator and allow the salmon to cure for 24 hours. After 24 hours, flip them around so that the bottom piece of salmon is on top, and refrigerate for another 24 hours.
After 48 hours, the salmon is ready to be sliced. Slice into paper-thin slices and serve with Mustard Sauce and toast.
Serving suggestion: toasts .
Mustard sauce for Gravlax and Herring:
In the bowl of an electric mixer fitted with a whisk attachment, mix the mustards, water, and sugar. Add the oil slowly, constantly whisking. If you add to much oil at the same time, it might break. Season with vinegar, salt, and pepper.