Preheat the oven to 180 C / fan 160 C / gas 4. Cut slits in the surface of the beef and insert the slices of garlic. Combine the ginger and mustard and rub over the beef.
Spoon over half the cranberry sauce. Pour in the beef stock.
Cover the meat with foil and cook in the preheated oven for approximately 2 hours depending on the degree of rareness that is required.
Baste occasionally. To make the cranberry sauce, combine the cranberry sauce with the redcurrant jelly and thyme, stir over a low heat until melted.
Add the port or wine and season to taste. Pour into a dish and keep warm.
Meanwhile, make the parsnip puree. Boil the parsnips until tender, then drain and mash. Add the horseradish sauce, seasoning and 2 tablespoons of water to thin down the consistency until it is easily spoonable. Remove the meat and keep it wrapped in foil.
To make the gravy, blend the cornflour with the remaining water and add to the roasting tin, bringing gently to the boil, stirring as it thickens. Serve with additional vegetables and Yorkshire puddings.