- Preheat the oven to Gas Mark 4, 180°C, 350°F.
- Heat the oil in large ovenproof pan with a lid. Add the onion wedges and cook for a further 1-2 minutes. Add Welsh Beef cubes and brown. Add the garlic, chestnuts, flour, ketchup, stock, ale, sugar, spice and season. Bring to the boil and then cover with lid or foil and place in oven for 2 hours until the meat is tender.
- Place prepared potatoes in a large pan, add just enough boiling water to cover and fast simmer with the lid on for about 10-15 minutes until soft.Drain potatoes and mash with a little milk.
- Heat the butter in small pan and slowly cook red onion slices for 2-3 minutes, add sugar and continue to cook until caramelised and browned. Add the onions to the mash and stir through the mashed potatoes.
- Remove the Welsh Beef from the oven, sprinkle with thyme leaves and pile the mash on top.
- Return to oven for about 20 minutes until mash is golden.