Oil-Poached Halibut With Fennel, Tomatoes, and Mashed Potatoes

Generously season fish with salt. Coat the bottom of a 3-to-4-quart saucepan or small pot with oil, then nestle fish pieces in, skin-sides down. Add just enough oil to fully submerge fish (about1 cup); attach a deep-fry thermometer to pan. Heat over medium until oil reaches 150 degrees. Reduce heat to low to maintain temperature (remove pan from heat briefly if it climbs above 150 degrees). Cook until fish turns opaque and is just cooked through, 8 to 12 minutes, depending on thickness. Remove with a fish spatula or slotted spoon, allowing excess oil to drip back into pot; transfer to a plate, skin-sides up, and loosely.cover with foil to keep warm.

While the fish is cooking; in a small pot, combine potatoes, 1 tablespoon salt, and enough water to submerge potatoes by about 2 inches. Bring to a boil, then reduce heat to medium; simmer potatoes until tender and easily pierced with the tip of a knife., 10-12 minutes. Drain; press potatoes through a ricer back into pot (or, for a chunkier potatoes, use a potato masher). Cover to keep warm.

Add fennel wedges, tomatoes, olives, and rosemary to pan, adding more oil to fully submerge ifnecessary. Increase heat to medium-high and cook until oil temperature reaches 210 degrees. Reduce heat to medium-low to maintain temperature and continue cooking until fennel is tender and easily pierced with the tip of a knife, 10 to 12 minutes. Remove vegetable mixture with a slotted spoon,reserving oil for potatoes.

Add milk and 1/4 cup reserved oil to potatoes, stirring until smooth. Season to taste with salt, pepper, and more oil. Remove skin from fish and serve over potatoes, with vegetable mixture and a drizzle of poaching oil.