Pan-seared halibut plated over a caramelized vegetable ragù with fingerling potatoes and mushrooms, finished with a rich butter sauce — an elegant, largely make-ahead entrée.
For the ragu: boil the potatoes in salted water about 20 minutes until fork-tender, then drain. Heat olive oil in a skillet, add the carrots and onions and cook about 10 minutes until caramelized. Add butter, potatoes, leek and sage and cook a minute more, then add the mushrooms and seasonings and cook 3 minutes more. Cover to keep warm.
For the sauce: heat olive oil in a small skillet, add the shallot and thyme and cook a minute. Add the bay leaf, peppercorns and vinegar and reduce 3-4 minutes. Off heat, whisk in the butter a little at a time until thickened, then strain.
For the fish: season lightly and dust with flour. Heat oil and butter in a nonstick skillet over medium heat and cook the fillets 3-4 minutes per side, about 7 minutes total, until lightly colored.
To plate, spoon the vegetable ragu onto each plate, top with a fillet, and nap with the butter sauce.
