Slow-roasting makes a beautifully tender, evenly cooked, not-one-bit-dry piece of fish. If you miss the 120° F, just-starting-to-flake mark and take it out late, it will still be good—even carryover cooking after taking it out of the oven won't outrun you, because there isn't much velocity behind it. This makes the technique perfect for dinner parties and newer fish cooks. 

Slow-Roasted Salmon (or Other Fish)

Serves: 4 
Prep time: 10 min 
Cook time: 35 min

• 1teaspoon extra-virgin olive oil
• 1 1/2pounds thick salmon fillet, or other fish like striped bass or cod (1 large fillet or four 6-ounce fillets)
• 2pinches kosher salt
• 1small bunch of fresh thyme sprigs (optional)
• 3tablespoons chopped fresh herbs, like chives (optional)
• 1/2cup Greek yogurt, for serving (optional)

1. Preheat the oven to 275° F. Brush a baking dish lightly with half the olive oil.
2. Arrange the fish fillet(s) skin side-down in the pan. Rub the top with the remaining olive oil. Sprinkle lightly with salt. Tuck half the thyme sprigs under the fish and place the remainder on top.
3. Roast for 15 to 35 minutes, until a two-pronged kitchen fork inserted in the thickest part of the fish meets with no resistance, the flesh separates easily from the skin, and is just beginning to flake when you poke into it. An instant-read thermometer should read 120° F. (Don't worry if the top of the fish has a slightly transparent, raw look; this is the result of the low roasting temperature. It will be cooked inside.)
4. Serve warm, room temperature, or cold. Remove the thyme sprigs and sprinkle with additional fresh herbs, like chives before serving, if desired. Serve with Greek yogurt mixed with more herbs, or another sauce of your choice.

https://food52.com/recipes/37487-sally-schneider-s-slow-roasted-salmon-or-other-fish