Start off with the stuffing. Heat the oil and butter in a sauté pan, add the onion and thyme and cook for about 5 minutes until the onion has softened. Add the bacon and cook for 2-3 minutes, then stir in the parsley and breadcrumbs and season to taste. Spread the stuffing over the beef slices and roll them up to enclose, securing them with a cocktail stick.
Preheat oven to 180°C/350°F/Gas mark 4. To prepare the casserole, heat the oil in a casserole dish with a lid over a high heat and sear the beef rolls until brown all over. Transfer to a plate and set aside.
Next, sauté the carrots in the casserole dish with the onion and celery for a few minutes until just catching colour. Add the tomato puree, wine, beef stock, bay leaf and thyme and bring slowly to the boil. Return the beef rolls to the casserole, cover and cook in oven for 1-1½ hours. Remove the beef and using a blender, blitz the sauce until smooth. Pass through a sieve and season to taste. If you think the sauce is a little too thin, just reduce down as necessary.
To serve, remove the cocktail sticks from the beef parcels and slice them on the diagonal. Arrange them on warmed plates, pour over the sauce and garnish with the parsley. Serve at once with with parsnip and potato mash.