Mix 1/4 cup mirin (Japanese sweet rice wine), 1/4 cup light brown sugar (do not substitute dark brown sugar), and ¼ c. soy sauce in a shallow dish that will hold 4 salmon fillets. Stir to dissolve sugar. Place the salmon in the dish and marinate for 5 to 10 minutes, turning once. Meanwhile, set a very large non-stick skillet on the stove and heat over medium-high heat. Place the salmon fillets in the hot, dry pan – nice sides down – and cook for a few minutes until nicely seared and coated with a rich brown glaze (keep a close eye on the pan; this happens quickly). Turn the fillets over, reduce the heat to medium, and add the marinade and 1/2 c. water to the pan. Cook 3 to 5 minutes more, until fish reaches desired doneness. If the sauce looks like it’s reducing or thickening too quickly, just add a bit of water a few tablespoons at a time. Do not let it burn. Transfer salmon fillets to serving platter or plates. If sauce is nicely reduced and thickened, turn off heat. If not, continue to cook over medium heat until desired consistency is reached. Add 1 tbsp rice wine vinegar to the sauce and stir. Pour the sauce over salmon fillets, top with scallions and serve. Serve over a white rice to complete your meal.