Cook the green beans in boiling, salted water for 3-4 mins, until just tender.
Drain and cool under cold running water. This can be done the day before just keep the beans covered in the fridge.
When youre ready to eat, heat the butter in a large frying pan until foaming, add the shallots and cook for 4-5 mins, until soft but not coloured. Throw in the beans and toss to coat. Cook for 1-2 mins until heated through, then season.
