In a medium bowl, combine softened unsalted butter, white miso paste, brown sugar, grated fresh ginger, minced garlic, and chopped green onions. Blend until smooth to create a creamy miso butter mixture.

Place salmon fillets on a clean cutting board. Spread the prepared miso butter over each fillet evenly.

Preheat oven to 375°F (190°C). Arrange salmon in a baking dish lined with parchment paper. Bake for 12-15 minutes until opaque and flakes easily.

Once baked, switch oven to broil and broil salmon for 1-2 minutes to caramelize the glaze.

For air fryer, preheat to 400°F (200°C). Line basket with parchment, place salmon fillets inside, and air fry for 9-10 minutes.

Transfer cooked salmon to a serving platter, drizzle with remaining miso butter, and garnish with green onions and sesame seeds.