Place potatoes in a large pan of boiling water. Cook with the lid on for about 20 minutes until potatoes are tender. Drain, add a little butter and milk and mash.
Preheat the oven to Gas Mark 4, 180ºC, 325ºF. In a large pan heat the oil and add the chicken, onion, garlic, leek and chorizo. Cook until chicken is lightly browned and leeks have softened. Add the remaining ingredients.
Simmer on the hob for 30 minutes (15 mins with lid on then 15 mins off). Place in individual ovenproof pots, roughly top with a mound of mash, sprinkle with cheese and cook for 20-25 minutes until topping is golden and chicken cooked through, with no pink showing.
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For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.