Preheat the oven to 200 degrees Celsius (392 degrees Fahrenheit) (fan).One of the best tips I've learned when it comes to preparing fish is
gourmet salting. Sprinkle coarse salt on both sides of the fish and let it sit on the kitchen counter for 5-10 minutes (depending on how salty you want it to be). I gave this salmon fillet 5 minutes. Rinse the salt off the fish with cold water directly under the tap. Then pat the fish dry with a clean tea towel/paper towel.Coarsely chop the pine nuts and parsley. Put them in a bowl with the soft butter and pesto.Grate the zest of your citrus fruit (be careful not to get the white part, it's bitter) and squeeze the juice into the mixture. Stir it well and season to taste with salt and pepper.Place the salmon skin-side down on a baking tray lined with baking paper.Spread the pesto butter evenly on top of the fish.Bake the fish for 15 minutes and it's ready to serve.