Dice carrot and onion finely and sauté in olive oil until onion is soft. Add the thyme and minced beef. Fry until meat is cooked and browned.
Add chicken stock along with tomato purée, ketchup and worcestershire sauce. Simmer for 25 minutes until the liquid has reduced. Add the peas to the mix and transfer to an oven-proof dish.
Preheat the oven to 180ºC/350ºF/gas mark 4.
Peel and cut the sweet potato into small chunks and cook until soft. Once cooked through drain the water. Mash until sweet potato is smooth. Season with salt and pepper and spoon the potato on top of the meat mixture and pop into the oven for approx 20 minutes until the potato is crisp on top.