Wash and roughly chop the bunches of dill, stems and all. Sprinkle the flesh side of each fillet half with the dill seeds and ground pepper.
Next, place one fillet half, flesh side up, in a dish just large enough to hold it. Place the chopped dill on top of this fillet, then cover with the second half, flesh side down. It will look like you have a huge raw fish-and-dill sandwich!
Cover the dish lightly with plastic wrap and let marinate at room temperature until the sugar-salt mixture has melted into the fillet (but no more than 6 hours. Skip this step entirely if you are making your gravlax in hot weather).
