Preheat the oven to 400°F (200°C). Grease a shallow baking pan with a thin layer of butter.
Rinse the salmon fillets and pat them dry with paper towels. Place the fillets skin-side down in the prepared pan.
Slice the lemon into 4 thin rounds, remove any seeds, then cut each round in half to make 8 halves.
In a small bowl, mix the dried thyme, turmeric, and salt until evenly combined. Sprinkle this spice mixture evenly over the tops of the salmon fillets.
Top each fillet with two lemon halves, arranging them over the spice-coated surface.
Using a grater, grate the very cold or frozen butter evenly over the tops of the fillets so small shreds cover the fish.
Cover the pan with aluminum foil or parchment and roast in the preheated oven for 15–20 minutes, or until the salmon reaches your desired doneness; check the center of the thickest fillet for doneness.
Remove the pan from the oven, uncover, and spoon the melted butter sauce from the tray over the fillets. Serve immediately.