1Wash and chop the runner beans. Place in a saucepan with salted water and bring to a boil.
2Cook the beans for about 10 minutes or until al dente. Drain and set aside.
3Meanwhile, add the potatoes and cook until tender.
4Heat a small skillet with a little butter and sauté the onion until translucent. Add the garlic and cook briefly. Add the runner beans to the pan and stir-fry for a few minutes.
5Meanwhile, mash the potatoes with a masher. Add a knob of butter and a splash of milk. Add the bean mixture and grated cheese. Season with salt, pepper and mustard.
