Heat the olive oil in a large pan and fry the onion, garlic, diced carrot and celery stick for 6-8 minutes. Stir in the minced lamb and cook for 3-4 minutes until browned, then add the sun-dried tomato paste and Worcestershire sauce. Stir in the beef stock and cover and simmer for 35-40 minutes until very tender. Season well. Mix the cornflour with cold water to a paste, stir in and cook for 1 minute. Serve over baked potatoes and top with grated cheddar.