Make the cure: in a bowl combine equal parts Sea salt and Sugar (enough to coat the fish), and crush or lightly grind a teaspoon or two of White peppercorns.
Prepare the fish: pat the Center-cut salmon fillet dry and place skin-side down on a large piece of cling film or in a shallow dish.
Cure the salmon: spread the cure evenly over the flesh, pressing it into the surface. Sprinkle a little Aquavit over the cure, then pile a generous handful of chopped Dill on top. Wrap tightly (or cover) and place a tray and a weight on top to press.
Refrigerate: let the salmon cure in the fridge for 24–36 hours, flipping once halfway through so the cure and dill contact all sides. The flesh will firm and become slightly translucent.
Finish the fish: unwrap, rinse the cure and dill off under cold water, and pat the salmon dry with paper towels. Thinly slice the gravlax at a shallow angle against the grain.
Make the dill-mustard sauce (hovmästarsås): in a bowl whisk together Swedish sweet mustard and Dijon mustard, stir in a splash of White wine vinegar, then slowly whisk in Neutral oil to create a smooth emulsion. Fold in plenty of finely chopped Dill and season to taste with Salt and more crushed White peppercorns if needed.
Serve: arrange thin slices of gravlax on slices of toasted Rye bread or a platter with the mustard-dill sauce on the side. Garnish with extra dill and enjoy.
