What you’ll need
Large saucepan or deep skillet
Slotted spoon or fish spatula
Poaching is a simple method of wet cooking that imparts clean and fresh flavors to fish while maintaining maximum moisture. There are many types of poaching liquids and all add their own unique properties. Wine, broth, milk, water, and even oil are just some of the possibilities. Whichever medium you choose, be sure to add aromatics like herbs, spices, aliums (garlic, onion, leeks), and/or citrus zest, and enough salt so the liquid tastes like the sea.
Fill a large saucepan or deep skillet with enough poaching liquid so the fish will be partly submerged. For the most effective poaching, make sure the liquid nearly covers the fillet. Bring the liquid to a boil, then reduce to a gentle simmer and add the fish. Cook until opaque, 5 to 7 minutes depending on the thickness of the fillet.
For oil-poached fish: Combine the aromatics, fish, and enough oil to fully cover the fish in a saucepan and bring to a gentle simmer. Cook until opaque, 5 to 15 minutes depending on the thickness of the fillet, the species, and the desired internal temperature (see How to Know When Fish is Done Cooking). Store any leftover fish in the oil (fully submerged) for up to 1 week. Or strain the oil and refrigerate it for another oil-poached fish.
For milk-poached fish: In a deep skillet, sauté aromatics like finely chopped leeks, shallots, or garlic in oil or butter until softened. Add enough milk to the pan so that the fish will be partly submerged. Season with salt and pepper, add fresh herbs, and bring to a simmer. Add the fish and cook until opaque, 5 to 7 minutes depending on the fillet size. Do not allow the milk to boil or add acidic ingredients like lemon juice or vinegar (or the milk may curdle).