1. Score each fillet with several diagonal shallow cuts on the skin side, about 1/8 in (3mm) deep.

2. Combine the salt, sugar, and peppercorns. Sprinkle a quarter of the mixture on the bottom of a shallow nonmetallic dish. Place one fillet, skin-side down, in the dish and sprinkle with half the aquavit and another quarter of the salt mixture. Spread 2 tbsp of the dill in an even layer over the fillet.

3. Sprinkle the flesh side of the second fillet with another quarter of the dry mixture. Place it, skin-side up, on top of the first fillet. Rub the remaining salt-and-sugar mixture over the skin and sprinkle with the remaining aquavit.

4. Cover the salmon with a sheet of wax paper. Top with a large flat plate or cutting board, and weigh it down with cans of food. Refrigerate for 24 hours, checking the salmon every 6 hours and draining off accumulated liquid from the dish. Turn the salmon over and refrigerate for another 24 hours, turning and weighing the salmon every 6 hours or so.

5. To make the mustard sauce, thoroughly whisk the mustard, oil, sugar, vinegar, sour cream, and salt in a bowl. Cover and refrigerate until chilled, at least 1 hour. Just before serving, add the dill.

6. To serve, scrape the seasonings and dill from the salmon. Place the salmon, skin-side down, on a cutting board. Slice the fish thinly on the slant, away from the skin. Sprinkle with the remaining dill. Serve with the mustard sauce and lemon wedges.