Place the two Huon Salmon fillets on a chopping board skin side down. Run your finger along the middle of the fish and remove any bones if your fish monger has missed them. Season with salt and pepper.
Place a large piece of baking paper, big enough to wrap the fish on a baking tray. Place fish on tray, top and tail, so head and tail are at opposite ends.
To make the stuffing place butter and oil in a fry pan on a medium heat. Add onion and garlic and cook until soft. Add spinach and cook until it softens. Remove from pan and drain on kitchen paper. Once cool squeeze out some of the moisture and season with salt and pepper.
To make the salmon mousse, place fish chopped up in small pieces in a food processor. Blend until it forms a paste. Then add egg whites, pinch of salt and process further. Finally add cream in a slow steady stream and blend until a smooth paste.
To stuff the salmon, spread the salmon mousse over one side of salmon (skin side down).
With a plastic scraper make sure the mousse is evenly spread. Place spinach all over the mousse. Sprinkle all the parmesan cheese and lots of cracked pepper. Place remaining side of salmon on top. Remember, top and tail. Wrap in the baking paper into a sausage and use kitchen string to tie. Cook at 150 degrees for 45 minutes. Once fish has cooked remove from oven and let it rest before unwrapping.
To serve, mix yogurt with lemon juice, salt and pepper and serve on the side.
Place fish on a serving plate, carefully remove skin and discard. Completely cover the fish with chopped chives and dill leaves. Sprinkle a little sea salt on top and serve.