Rinse the salmon fillet under cold running water, drain, and pat it dry thoroughly with paper towels.
Place it on a cutting board and check that all the pin bones have been removed by the fishmonger. If not, you can remove them using tweezers.
Using a mortar and pestle, coarsely crush the peppercorns, pink peppercorns, and fennel seeds. Finely chop half of the fresh dill.
In a bowl, mix the salt, sugar, chopped dill, and crushed spices to create the curing mixture.
In a baking dish large enough to hold the entire salmon fillet, spread a layer of the salt, sugar, and spice mix. Add a bit more around the edges, this will help cover the sides of the fish.
Cover the flesh side of the salmon completely with fresh dill sprigs, then gently place the fillet flesh-side down onto the salt mixture.
Bring the salt mixture up around the sides to ensure the entire fillet is well covered. Wrap tightly in 2 to 3 layers of plastic wrap, pressing it directly against the fish.
Place a dish or tray on top of the wrapped salmon along its full length, then add a weight to apply gentle pressure. Refrigerate for 24 to 72 hours (1 to 3 days), depending on the thickness of the fillet. I left mine for 48 hours.
Each day, drain off the liquid released by the salmon. The fillet will gradually take on a lovely orange hue and become firmer in texture.
The curing time will depend on the thickness of the fillet and the desired level of dryness.
After the second day, remove the salmon from the dish and rinse it briefly under cold running water to remove excess salt.
Place it on paper towels and pat it dry thoroughly on both sides. Then, using a knife, gently scrape off the marinade and dill sprigs.
You can enjoy it immediately, or for an even better texture, let it air-dry uncovered on a rack in the fridge for a few more hours.
Place the salmon gravlax on a serving platter or slice it thinly on the bias, leaving the skin on. Use a sharp knife for best results.
Arrange the slices neatly on a plate, drizzle with a little olive oil, and sprinkle with fresh dill.
I served it whole on a charcuterie board, slicing only part of it beforehand. The rest was sliced at the table. I also sprinkled a few pink peppercorns on top for decoration.