For the scallops:
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.
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.
Return the pan to medium heat. Add a piece of the butter (1/2 Tbs.) and the shallots and sauté until the shallots begin to soften, about 1 minute. Add the vermouth or wine and simmer until reduced by about half, another 1 to 2 minutes. Add the herbs and lemon zest. Reduce the heat to low, add the remaining butter, and whisk constantly until the butter melts into the sauce. Return the scallops and any accumulated juices to the pan. Gently roll the scallops in the sauce to warm them through. Taste for salt and pepper and serve immediately with lemon wedges on the side to squeeze over the scallops.