The flavors here are simple and delicate, so make sure your fish is exceedingly fresh. Same with your butter. If you don't have access to nasturtiums, you can substitute a tablespoon or two of your favorite fresh herbs, like Italian parsley, tarragon, and chives, well chopped.
12 nasturtium flower petals
1 stick unsalted butter, at room temperature
Zest from 1 lemon
Kosher or sea salt, to taste
Freshly ground black pepper, to taste
(4) 4-ounce pieces of cod, haddock, or halibut, each about 1-1/2-inches thick
Swirl the flowers in a large bowl of cold water and gently swirl them around to release any dirt. Remove the flowers from the water and place them on a clean tea towel or paper towel until completely dry.
Place the softened butter, lemon zest, and a pinch of salt and pepper in a medium bowl. Finely chop the nasturtium petals and add them to the bowl. Gently mix until everything is well combined, with visible flecks of flowers throughout. Transfer the butter mixture to a piece of plastic wrap and roll into a log, twisting up both ends to enclose. Refrigerate the butter until firm, at least 1 hour.
Preheat the oven to 375°F. Place the fish in a large baking dish and add about 2 tablespoons of water to the dish. Roast uncovered until the fish is opaque and cooked through, about 12 minutes. Meanwhile, remove the butter from the refrigerator and cut 4 slices from the log.
Transfer the fish to a plate lined with paper towels to remove any excess moisture, then transfer to a serving platter or individual plates. Set a slice of butter on top of each piece of fish. Serve warm.
Reserve the remaining butter well-wrapped for another use (like spread on good French bread with sliced radishes).
Source: Adapted from The Coastal Table by Karen Covey
