Onglet and hanger steak are one and the same, and I think it packs a much beefier punch.
Dry the steaks out in the fridge, rub them with a little duck fat and salt them lightly. No pepper until the heat is down, because it burns. Sear them in a very hot dry pan until charred on all sides, then lower the heat and cook for 5 minutes. Towards the end, add butter and baste. Rest them on a warm tray, then slice. Brilliant with salsa verde. And switch your fan on, because it gets smoky!