Pat dry the salmon to remove any moisture with a paper towel. Cut the salmon into 4 pieces.
Distribute shio koji to all sides of salmon, including the skin. Cover with plastic and refrigerate overnight. If you want to freeze the uncooked salmon, you must store the marinated salmon in an airtight freezer bag and store in the freezer for up to a month.
To Cook Salmon
Line a baking sheet with foil and preheat the oven to broil. When broiling, you don't control the temperature in the oven; instead, you control the distance between the broiler and the surface of the food. If you don’t have a broiler, preheat the oven to 425ºF.
Remove the shio koji from the salmon fillet as it gets burn easily. Place the salmon on the prepared baking sheet, 1-2 inches apart from each other.
Broil the salmon for 10 minutes. When the top is nicely charred, flip so the side of the salmon is now up. Put the salmon back in the oven and bake for another 5-8 minutes until the instant-read thermometer reads 165ºF – the safe internal temperature of the salmon. To bake, place the salmon in the preheated oven for 15 minutes.
Serve warm or at room temperature.
To Store
You can keep the left overs in an airtight container and store in the refrigerator for up to 3 days and in the freezer for1 month.