Crush the dill with the coarse salt and add the brown sugar. Sprinkle the salmon fillets with the Szechuan peppercorns. Cover with the dill mixture and splash with vodka. Sandwich the fillets together, tail-to-tail, and cover with plastic wrap. Cover the salmon with another plate and something that weighs about a pound. Refrigerate for 24 hours. After that time, the flesh will have lost its translucence. Rinse under cold water and pat dry.
For the mustard sauce:
Combine the mustard, brown sugar and lemon juice. Slowly whisk in the olive oil and stir in the chopped dill and grated horseradish to taste. Slice the gravlax thinly on the bias and without the skin. Serve with crackers and the mustard sauce.