Cut the stems off the Brussels sprouts and slice them in half. Peel the pearl onions and slice in half. Cut the bacon into 1 cm slices.

In a large frying pan or wok, melt the butter on medium heat and add the sprouts, onions and bacon all at the same time. Sprinkle in the salt, pepper and rosemary. Pan-fry for 7 minutes or until the bacon is cooked and the sprouts can be pierced through with a fork.