In a bowl, combine marinade ingredients and whisk well until combined. Add salmon to the bowl or place everything in a Ziploc bag, then refrigerate and marinate for 30 minutes.
Boil potatoes in lightly salted water until tender.
In a skillet, heat cooking oil (if you have unsalted butter or ghee use that) over medium heat. Saute leek until soft. Stir regularly.When potatoes are ready, mash potatoes, leek, egg, salt, nutmeg, and black pepper until well combined. Add a splash of milk or water if needed.
Preheat the broiler/grill in your oven.
Remove salmon from the marinade. Brush with marinade and sprinkle with a little bit of salt and pepper, then place directly on the wire rack, under the broiler/grill, skin down. Place wire rack over baking sheet to catch baking fluids from the salmon that may drip down.
Cook for 10-15 minutes, depending on the salmon's thickness, until opaque and easily flakable with a fork. You can flip the salmon halfway through cooking if desired.