In a large mixing bowl, whisk together all marinade ingredients. Pour mixture into an immersion blender and blend until smooth.
Place salmon filets into gallon zip top bag and pour the marinade in. Close the bag and marinate in the fridge for 2 hours.
Preheat oven to 425 F. Line a large baking sheet with parchment paper.
Remove salmon from marinade, do not discard marinade. Place salmon filets skin side down, onto prepared baking sheet.
Bake in oven for 18-20 minutes.
Meanwhile, place marinade in a medium saucepan over medium high heat. Make a slurry from the cornstarch and water and add it to the saucepan. Cook, stirring occasionally, until mixture begins to thicken. Remove from heat.
Remove pan from oven and brush the salmon filets with the thickened marinade. Return to the oven and bake an additional 8-10 minutes.
Remove from oven and brush lightly with thickened marinade and garnish with sesame seeds and sliced green onions.
Notes
When choosing salmon from the grocery store, steer clear of any fish with gray areas or blemishes. Filets should be firm and have a vibrant pink color. Center-cut salmon provides uniform thickness between your filets. Use a sharp chef’s knife to slice into smaller filets.
You can use frozen salmon filets, but be sure to thaw them before beginning.
The type of miso paste you use is up to your preference. Light-colored miso pastes have more of a salty-sweet profile, while darker pastes are deeply savory due to being fermented longer. We opted for white miso paste in ours but any kind will work. I would suggest using low-sodium soy sauce if you choose to use a dark miso.
Always cook fish with the skin side down. If you place the fish skin side up, it will cook and begin to flake, making it fall apart as you lift it.