a few drops of truffle oil (or truffle flavoured oil)
Drizzle the steak with oil and season with salt & pepper.
Braai over hot coals or grill in a piping hot griddle pan, until cooked to your liking (3,5 minutes a side for a 3 cm thick steak, for medium rare). Remove and leave to rest while you prepare the mushrooms.
Heat the butter over high heat in a pan, then fry the mushrooms with the thyme until golden brown on all sides. Season with salt & pepper.
Remove from the heat, then add a few drops of truffle oil and stir to mix.Top the rested steak with the hot truffle mushrooms and serve at once.