The chanterelle mixture may be prepared a day in advance.
6 tbsp. extra-virgin olive oil
1 lb. (about 7 cups) fresh chanterelles,
trimmed and quartered
2 large shallots, peeled and minced
2 cloves garlic, peeled and minced
1 tbsp. fresh thyme leaves, chopped
3 tbsp. aged sherry vinegar
Salt and freshly ground black pepper
1 tbsp. butter
4 8-oz. fresh center-cut cod filets
1. Heat 4 tbsp. of the oil in a large skillet over medium-high heat. Add mushrooms and cook, stirring often, until mushrooms are tender and any liquid has evaporated, 10-15 minutes. Add shallots, garlic, thyme, and 2 tbsp. of the vinegar. Season to taste with salt and pepper, and cook for 2 minutes more. Remove from heat and set aside to cool slightly, then add the remaining 1 tbsp. vinegar. Mix well. Transfer mushrooms to a bowl and set aside for 1 hour to allow flavors to develop.
2. Preheat oven to 375°. Brush cod filets with 1 tbsp. of the oil, then generously season with salt and pepper. Heat butter and the remaining 1 tbsp. oil in a large ovenproof skillet over medium-high heat. Sear cod until a good browned crust has formed, about 3 minutes per side. Transfer skillet to the oven and roast cod until cooked through, another 10-15 minutes.
3. Transfer cod to a platter and spoon room-temperature mushrooms and their juices on top. Garnish with extra sprigs of thyme, if you like.