Set fish on a large plate and sprinkle generously on both sides with salt and pepper. Drizzle olive oil over fish sufficient to cover all surfaces and allow fish to marinade for 5 to 10 minutes. Heat a large skillet (nonstick works well) on high heat. Just as skillet starts to smoke add fish and immediately reduce heat to medium. Cook fillets on 1 side until fish releases easily from pan and is golden brown and slightly crispy. Turn fillets and continue to cook until fish is just cooked through, time will depend on thickness of fillets. If you have particularly thick fillets, you may need to reduce heat to very low and cover pan to finish cooking. Serve fish immediately with Triple Mustard Vinaigrette, and Brown Butter Brussels Sprouts.
Brown Butter Brussels Sprouts:
In a large skillet heat butter until it is foamy and just starts to brown on the edges. Add cipollini and cook on high heat, tossing frequently, until cipollini are nicely browned and just starting to get tender. Add Brussels sprouts, and cook, tossing frequently, until they are well browned on the cut sides and just starting to turn bright green. Add enough chicken stock to just cover Brussels sprouts and add bay leaf. Bring stock to a simmer and cook until vegetables are just tender and liquid has reduced nearly all the way. Add more stock to pan if liquid reduces before vegetables are tender. Add salt and pepper, to taste, and stir in thyme. Serve Brussels sprouts in their sauce.
Triple Mustard Vinaigrette:
Place mustard seed in a small skillet and cook over medium-high heat, shaking pan frequently, until seeds start to pop. Immediately transfer seeds to a small bowl. Add shallot, vinegar, grain mustard, honey and dry mustard and whisk to combine. Add some salt and pepper and allow mixture to sit for 5 to 10 minutes to meld flavors and dissolve salt. Whisk in olive oil, then add parsley and adjust seasoning, to taste. Serve at room temperature.