In a bowl, combine the sea salt, granulated sugar, and crushed black peppercorns.
Place the salmon fillet on a large piece of plastic wrap, skin side down.
Sprinkle the salt, sugar, and pepper mixture evenly over the salmon, ensuring it is well coated.
Spread the chopped fresh dill over the top of the salmon. If using, place the lemon slices on top of the dill.
Wrap the salmon tightly in the plastic wrap.
Place the wrapped salmon in a shallow dish or baking tray to catch any liquid that might seep out during the curing process.
Place a heavy object, such as a cutting board or another tray, on top of the wrapped salmon to weigh it down.
Refrigerate the salmon for at least 24 to 48 hours. The longer the salmon cures, the more intense the flavor will be.
Turn the salmon over every 12 hours, redistributing the curing mixture and any accumulated liquid.
After the curing period, remove the salmon from the refrigerator.
Unwrap the salmon and rinse off the curing mixture under cold water.
Pat the salmon dry with paper towels.
Place the salmon fillet skin side down on a cutting board.
Using a sharp knife, slice the salmon thinly at an angle, separating it from the skin.
Serve the gravlax with traditional accompaniments such as mustard-dill sauce, rye bread, or crispbread.
Enjoy your meal!