Prepare the ingredients for the sauce. Remove the tough abductor muscle from the side of each scallop (some scallops are sold with the muscle already removed). If you feel any grit on the scallops, rinse them under cold water. Pat the scallops dry with paper towels; surface moisture impedes browning. 

Dry the scallops well to ensure a golden crust.

Heat a 10- or 12-inch nonstick skillet over medium-high heat for 1 to 2 minutes. Add the oil and butter, if using, and heat until quite hot. Pat the scallops dry once more and put them in the pan in a single, uncrowded layer. Season with salt and pepper and let sear undisturbed until one side is browned and crisp, 2 to 4 minutes. Using tongs, turn the scallops and sear until the second side is well browned and the scallops are almost firm to the touch, 2 to 4 minutes. Take the pan off the heat, transfer the scallops to a plate, and set them in a warm spot. Let the pan cool for a minute before you make the sauce.

For a deeply golden sear, use medium-high heat and don’t crowd the pan. To avoid tearing the scallops while turning them, use a nonstick skillet and handle them gently.