Bangers and mash may be the meat and potatoes, but this cozy Brit classic hangs on the onion gravy. Great bangers and mash with onion gravy, the iconic British pub staple, revolves around plump, well-browned links napped with an ultrasavory sauce. Searing the sausages ensured that the links developed attractive, flavorful browning; steaming cooked them through gently so that they were plump and juicy. Adding the onions (thin-sliced so that they softened quickly) to the pan to steam with the sausages jump-started their cooking. Continuing to sauté them after the sausage came out further softened them and caramelized their sugars; doing so also developed a deep, flavor-packed fond on the bottom of the skillet. Deglazing the pan with a highly seasoned beef broth captured the fond, and simmering the onions in the broth tenderized them more and concentrated the flavor of the gravy. A cornstarch slurry and butter, whisked in just before serving, gave the gravy the requisite viscosity, shine, and richness.