STEP 1 Boil the potatoes for 15 mins or until tender. Drain, then mash. STEP 2 Heat the milk and half the butter in the corner of the pan, then beat into the mash, along with the wholegrain mustard. STEP 3 Gently fry the spring onions in the remaining butter for 2 mins until just soft but still a perky green. Fold into the mash and serve. Great with gammon or to top a fish pie.