Mix together sugar, salt, pepper, fennel, caraway and juniper in a mortar or heavy bowl and grind slightly with a pestle or other heavy object; set aside.
Rinse fish filets in cold water and pat dry with paper towel. Lay one filet skin-side-down in a glass baking dish. Rub and pack some of the sugar mix on both sides.
Lay the fresh dill on the flesh side of the filet. Cover the other filet flesh side with the sugar mix and put on the first filet like a sandwich.
Top the skin side of the second filet with remaining sugar mix, being sure to also coat the edges of the fish.
Sprinkle on about a tablespoon of the aquavit or gin and wrap the entire dish tightly with plastic. Put a heavy weight on top and refrigerate for 12 hours.
Unwrap and flip the fish “sandwich” over. Baste all sides with the brine that is developing in the pan and sprinkle with another tablespoon of gin.
Wrap, weight and refrigerate and repeat the entire process again in 12 hours. Keep this going for at least 48-72 hours (but don’t use more than the ¼ cup of alcohol for sprinkling).
Unwrap the fish, discard the dill and rinse the filets under cold water and pat dry with paper towel.
Place the gravlax skin side down on a cutting board. With a long, very sharp bladed knife, slice gravlax against the grain on the diagonal into thin pieces.
Refrigerate any remaining gravlax, wrapped in plastic, for up to 2 weeks.