Lay two layers of cling film, long enough to wrap around the salmon and overlap, out on your bench. Spread out half of the salt and botanical mixture and place the salmon fillet on top, bottom side down. Cover the top of the salmon with remaining salt mixture. Your salmon should be completely covered with the salt mixture, just like a salt crust. Wrap everything tightly in the cling film and place in a deep-sided tray. Place another small flat tray on top and weigh down with whatever you have to hand e.g. a can from the pantry. Just enough weight to press the salmon down. The salmon will leak out some moisture, so keep this in mind. Refrigerate for 24 hours.