Start by combining the white miso paste, sugar, mirin, sake, ginger, and sesame oil in a bowl. Mix until smooth. The sugar should dissolve, creating a luscious marinade that envelops your fish.

Pat the black cod fillets dry. This helps the marinade adhere better. Layer the marinade on both sides of each fillet generously. Place the fish in a resealable plastic bag or dish and ensure it’s fully coated. Let it marinate in the refrigerator for 24 hours. This step intensifies the flavor—it's worth the wait!

When you’re ready to cook, preheat your oven to 400°F (200°C). An even temperature is vital for that perfect browning you want.

Lightly grease a baking sheet with cooking spray or oil. This prevents the fish from sticking and simplifies cleanup.

Remove the fish from the marinade (don’t rinse it off!) and place it on the baking sheet. Bake for 10-12 minutes. You can broil it for the last 2-3 minutes for an irresistible caramelized crust.

Once cooked, let the fish rest for a couple of minutes. Serve it warm. Presentation matters—adding a sprinkle of sesame seeds or sliced green onions elevates the dish visually.