875 g (1¾ lb) potatoes, peeled and cut into chunks
50 g (2 oz) butter
2–3 tablespoons wholegrain mustard
Place the sausages, onions and leeks in a large roasting tin, toss with the rosemary and oil and season with pepper. Roast in a preheated oven, 200˚C (400˚F), Gas Mark 6, for 25 minutes, tossing a couple of times during the cooking time.
Meanwhile, cook the potatoes in a pan of boiling water for 12–15 minutes, until tender.
Drain the potatoes, return to the pan and mash with the butter until smooth. Stir in the wholegrain mustard.
Divide the mustard mash between 4 warmed shallow bowls. Spoon over the sausages, roast vegetables and any juices from the roasting tin.