Bring a large pan of salted water to the boil and cook the sprouts until tender, about six to eight minutes. Drain into a colander and place over the pan to steam dry. Place the same pan over a medium-high heat and add the butter and a splash of oil. When hot, add the sprouts. Shake the pan until they are all coated in butter then leave them to fry until they are golden. Shake the pan again, leave another few minutes, then turn the heat down to low and add a little pepper. Continue cooking for another few minutes until they are a nice even colour, then check the seasoning and keep warm.