Heat half the oil in a frying pan over a medium heat. Add the sliced garlic clove, thyme and mushrooms and cook for around 5-6 minutes, until the mushrooms are golden. Splash in some madeira and stir through the crème fraîche. Season and keep warm.
Heat a griddle pan over a medium to high heat. Brush the steak with the remainder of the oil and season well with black pepper. Sear on the griddle for 4-6 minutes (depending on how you like your steak cooked), turning halfway through. Remove from the pan and leave to rest, covered, for a couple of minutes.
While the steak is resting, griddle the bread until toasted. Rub with the remaining whole garlic clove.
Serve the steak on the toasted bread with the mushroom sauce drizzled over the top.