Transfer steak to a plate and pour off all but 1 tablespoon fat from skillet (use caution; handle will be very hot). Return skillet to stovetop over medium heat and add shallot, then cook, stirring, until softened, about 2 minutes. Add mushrooms and cook, scraping up any brown bits, until mushrooms are soft and any liquid they give off has evaporated, about 8 minutes. Add wine and any meat juices accumulated on plate, then boil until liquid is reduced by half. Stir in oyster sauce and butter and remove from heat.