In a small mixing bowl, combine the miso paste, soy sauce, brown sugar, mirin, and sesame oil and stir until everything is combined.
Place salmon fillets in a sealable container and season with salt and pepper. Then add the marinade making sure that all sides are coated in the miso paste mixture. Then cover the container and marinate for 2-3 hours in the fridge Tip: If you are short on time you can reduce the marinating time to as low as 20 minutes. However, the closer to two hours the better.
Once the salmon is done marinating, adjust the oven rack so it's around 9 inches (23 cm) from the heating element and set the oven to broil on high.
Place the salmon fillets skin side down on a baking sheet lined with foil and sprayed with cooking oil. Be sure to remove any excess marinade as it may burn in the oven. Cover any thin spots on the salmon fillet with foil to prevent it from burning.
Broil salmon for around 8-10 minutes, or until the top of the salmon is well charred.
Serve and enjoy!