Preheat the oven to 375°F. Score the skin of the sea bass three times to help the filet lay flat. Season with salt. Place on a baking sheet, with a piece of parchment for easy cleanup if you have it. When done, it flakes easily and a fork slides through easily.
While the fish is baking, make the sauce. In a small saucepan or skillet, sauté the shallots in the oil until golden, 5 to 7 minutes. Mix in the capers and lemon juice. Take the pan from the heat, and whisk in the butter, one piece at a time, until the sauce is creamy.
Sauté the garlic in a film of olive oil for less than a minute. Add spinach and saute until cooked.
To plate, place the spinach on the plate, top with the black sea bass. Spoon sauce over and around the fish.
Catherine Walthers, Bluedot’s food editor, is a Martha’s Vineyard-based writer, culinary instructor, and private chef. A former journalist, she is the author of 4 cookbooks, including Kale, Glorious Kale, Soups + Sides, and Raising the Salad Bar. She wrote an environmental guidebook called A Greener Boston published by Chronicle Books in 1992. Follow her on Instagram @catherine_walthers.