How to Make It
Preheat the oven to 400°. In a medium saucepan, bring the orange juice to a boil. Simmer over moderate heat, stirring, until reduced to 3/4 cup, 8 minutes. Whisk in the miso, lime juice, ginger, shallot and togarashi. Cook for 1 minute, then remove from the heat; gradually whisk in 1/4 cup of the olive oil. Season the sauce with salt and pepper and keep warm over very low heat.
Butter a large ceramic baking dish. Season the halibut fillets with salt and pepper and arrange them in the dish. Gently rub the fish with the 2 tablespoons of softened butter. Add 1/4 cup of water to the dish and bake for 8 to 10 minutes, until the fish is just cooked through.
Meanwhile, in a medium bowl, toss the fennel and tomatoes with the remaining 1 tablespoon of olive oil. Season the salad with salt and pepper.
Transfer the fish to plates and mound the fennel salad alongside. Drizzle the fish with the warm orange-miso sauce and serve.
Togarashi is available in the Asian section of many supermarkets and at Japanese markets, or online at amazon.com.