Combine the sugar, salt, crushed juniper berries and pepper in a bowl and mix together.

Arrange about half the dill (stems included) in the center of a rimmed baking sheet or other shallow pan (make sure the pan will fit in your refrigerator), covering an area the size of your fillet.

Place the salmon skin side up on a cutting board and make 4 long but shallow cuts through the skin. Sprinkle about one-third of the sugar-salt mixture over the skin side of the fish, then place the fish skin side down on the bed of dill. Distribute another third of the sugar-salt mixture over the flesh side of the fish, then top with the remaining dill sprigs, making sure they cover the surface evenly. (Reserve the remaining salt mix.)

Wrap the fish and baking sheet tightly in plastic wrap and place a heavy pan on the fish to press it down, making sure the weight is evenly distributed. Refrigerate for 24 hours.

The next day, remove the fish from the refrigerator, unwrap, pull back the dill sprigs on the top (reserve them), and baste the fish in the juices that have accumulated in the pan. Sprinkle the top of the salmon with the remaining sugar-salt mixture and return the dill sprigs, arranging them neatly. Wrap with a fresh piece of plastic and place the heavy pan back on top. Return the salmon to the refrigerator for another 12 hours.

After the 12 hours, remove the fish and gently rinse off the salt mixture with cool water, discarding the dill. Dry the salmon thoroughly by blotting it gently with paper towels. Keep tightly wrapped and refrigerated until ready to serve.

To serve, sprinkle the gravlax with the chopped dill, if using, and thinly slice the fillet at an angle, leaving the skin behind, slicing only as much as you plan to serve. Wrap any unsliced fish tightly in plastic wrap and keep in the refrigerator for up to 1 week.