Dry and season: Pull scallops from the fridge 20 minutes before cooking. Pat aggressively dry with paper towels — multiple rounds if needed. Any surface moisture and you get steam, not sear. Season with 1 teaspoons kosher salt and 0.3 teaspoons black pepper right before the pan.
Get the pan ripping hot: Heat a heavy skillet — cast iron or stainless — over high heat until it just begins to smoke. Add 2 tablespoons duck fat and let it shimmer and coat the pan.
Sear first side: Add scallops in a single layer with space between them. Do not move them. 90 seconds to 2 minutes until a deep golden crust forms on the bottom.
Flip and finish: Flip once. 60-90 seconds on the second side. They should feel slightly firm but still have give. Pull them immediately — they carry over.
Finish with lemon and marjoram: Off heat, squeeze half the 1 lemon over the pan, let it sizzle for 5 seconds, spoon the pan drippings over the scallops. Garnish with 3 fresh marjoram sprigs leaves stripped from the stem.