In a medium bowl, combine 6 tablespoons of softened unsalted butter with 3 tablespoons of white miso paste, 1 tablespoon of brown sugar, 2 teaspoons of grated fresh ginger, and 1-2 cloves of minced garlic. Mix everything together using a fork or spatula until well blended.

Using a butter knife or spatula, evenly spread the prepared miso butter mixture over each salmon fillet. Ensure the butter mixture reaches all corners of the fillet.

Preheat your oven to 375°F (190°C). Place the coated salmon fillets on a baking sheet lined with parchment paper and bake for 12-15 minutes, or until opaque.

For the air fryer, preheat it to 400°F (200°C) and carefully arrange the salmon fillets in the basket. Cook for 9-10 minutes until flaky.

Transfer the cooked Miso Butter Salmon to a serving platter, drizzle with remaining miso butter, and garnish with green onions and sesame seeds.