Preheat your oven to 375°F and line a sheet pan with foil.
Add butter, miso paste, 1 tablespoon chopped chives, lemon zest, and garlic powder to a bowl. Stir by hand or miix with a hand mixer on medium speed until smooth, about 1 to 2 minutes. Scrape down the sides as needed.
Pat salmon fillets dry and season with salt and pepper.
Heat a skillet over medium-high heat. Add 1 tablespoon of the miso butter and let it melt.
Add the salmon fillets skin-side up. Sear until nicely browned on the bottom, about 3 minutes.
Transfer the fillets to the prepared sheet pan, browned side up. Spread 1 tablespoon of miso butter evenly over the tops.
Bake for 8 to 10 minutes per inch of thickness, until the salmon is just cooked through. (10 minutes is usually right for a standard fillet.) If the top isn't browned to your liking, switch on the broiler and slide the pan under it for about 1 minute. Watch it closely!
Serve topped with an extra pat of miso butter if desired, and garnish with a tablespoon of chopped chives.
Notes
Storage Tips: Leftover salmon keeps in the refrigerator for up to 2 days in an airtight container. Reheat gently in a low oven (around 275°F) or in a skillet over low heat to avoid drying it out. Flaked cold miso butter salmon is also excellent over salad or tossed with pasta the next day.Expert Tips:
If you’re making this miso salmon dish ahead of time, roll the miso butter into a log and wrap plastic wrap. Then refrigerate. Let it soften a bit at room temperature before you’re ready to make the salmon.
Dry the salmon well before seasoning. Patting the fillets dry with paper towels makes a real difference for getting a good sear. Excess moisture steams the fish instead of browning it.
Don't overcook it. Salmon is at its best when it's just cooked through, still slightly translucent in the very center. Pull it from the oven as soon as it flakes easily.
Make the miso butter ahead. You can make a double or triple batch and keep a log in the fridge or freezer. It's great on roasted vegetables, pasta, steak, and chicken, so it won't go to waste.