Grilled Bavette, Mushroom Beurre Rouge

Bavette d’aloyau (flap steak), cut from the bottom sirloin of grass-fed beef.  Marinated for 2 days in olive oil, fresh garlic, rosemary and thyme, then quickly grilled over high heat to rare-medium rare.  Rested, then thinly sliced across the grain and served with a reduction of dry red wine, red wine vinegar and shallots with knobs of cold, pastured butter whisked in to form an emulsion.  Finished with Fleur de Sel and freshly-ground black pepper..