Lightly season scallops with salt and pepper. Add butter and olive oil to large pan over medium heat. Once hot (but not smoking), add scallops in a single layer, taking care not to over-crowd them. Let sear for about 2 minutes before flipping and searing for another 1-2 minutes, until golden brown on both sides. Remove to a plate and tent with foil to keep warm while preparing the rest of the sandwich.