Instructions

1. Line a baking sheet with aluminum foil. Fit a wire rack onto the baking sheet and coat with cooking spray. Pat 4 (6-ounce) salmon fillets dry with paper towels. Season all over with 1 teaspoon kosher salt. Place skin-side down on the rack and let sit for 20 minutes at room temperature. Meanwhile, arrange a rack about 6 inches from the broiling element and heat the oven to 400ºF. Make the sauce.
2. Place 1/3 cup mirin, 1/3 cup sake, 1/4 cup soy sauce, and 2 tablespoons packed brown sugar in a small saucepan and bring to a boil over high heat, stirring to dissolve the sugar. Reduce the heat to medium-low and simmer until the sauce is reduced by about half to 1/2 cup, 12 to 15 minutes.
3. Turn off the heat. Transfer about 2/3 of the sauce into a small serving bowl for finishing and serving. Reserve the remaining for brushing the salmon.
4. Generously brush the tops and sides of the salmon with some of the sauce from the saucepan. Roast for 6 minutes.
5. Remove the salmon from the oven. Turn on the broiler. Brush the salmon with sauce again. Return the baking sheet to the oven and broil until the salmon is just cooked through and flakes easily in the thickest part, and the top is browned in spots, 3 to 7 minutes more. For medium-rare salmon, cook to an internal temperature of 120ºF; for medium salmon, cook to 125ºF. Watch carefully during broiling for burning. Discard any remaining sauce left in the saucepan.
6. Let rest for 2 minutes. Spoon some of the serving sauce over the salmon and garnish with 1 thinly sliced medium scallion and white sesame seeds if desired. Serve with the remaining sauce if desired.