Heat 1 tablespoon EVOO in a pan over medium-high heat. Melt butter into oil; add mushrooms and brown well, 12-15 minutes. Add shallots, garlic and herbs, and cook to soften a few minutes more. Add sherry, let reduce for 2 minutes, add stock and reduce by half.
Rub meat with a drizzle of oil. Heat grill, griddle pan or cast-iron skillet to medium-high heat. Char meat in the pan or on the grill then season liberally and cook 8 minutes for rare, 12 for medium, turning once. Let rest and slice.
Butter toast and cut into diagonal halves. Arrange toast points on dinner plates, top with sliced steak, lots of cheese crumbles and sherry mushrooms. Serve with a cress salad alongside.