Thaw sockeye salmon that has been frozen for at least 1 week. Remove backbone and ribs, but leave the skin. Combine salt, sugar, and pepper in a small dish, then rub into flesh of each fillet, making sure to spread mixture uniformly. Layer dill over 1 fillet, then replace the other fillet on top. Put stacked fillets in a flat-bottomed glass or ceramic casserole pan large enough to allow fillets to lie flat. Cover loosely with plastic wrap and place another dish or a clean cutting board about the same size as the fillets, over the top of the fillets. Make sure the dish/board doesn?t touch the sides of the lower pan. Place a 3 to 5 pound weight on top to compress fillets. Place in refrigerator to allow a marinade to start forming. Once a day, flip fillets, ensuring both are well soaked in marinade. Replace the plastic wrap and weight, then return to refrigerator. After 4 to 5 days, the process is complete and the gravlachs will be ready. The weight flattens the fillets, and the loss of moisture produces the distinctive firm texture of lox.
The gravlachs can be eaten right away. Or slice into halves or thirds, wrap securely, and freeze.
To serve, cut thin slices but leave skin behind. This is generally easiest if the gravlachs is still slightly frozen.
Mild Mustard-Dill Sauce: Combine mustard, sugar, and flour, then add enough vinegar to make a thick sauce. Add 1 tablespoon of mixture to mayonnaise, then stir in chopped dill and whipped cream. Present in a small dish with a serving spoon alongside the gravlachs.
Serving Suggestions: Serve atop wafer crackers or melba-style toast with cream cheese, finely chopped onions, capers. For a more traditional twist, serve mild mustard-dill sauce.