- Preheat the oven to Gas mark 4-5, 180-190°C, 350-375°F.
- Place the topside joint on a chopping board, make several slits over the joint and season and rub with the mustard. Push the garlic slivers into the slits.
- Place the joint on a metal rack in a large roasting tin and open roast for the preferred, calculated cooking time, basting occasionally with any rich beefy juices.
- In a small bowl, mix together the marmalade, orange juice and parsley. Divide the mixture between two separate bowls.
- 20-25 minutes before the end of the cooking time remove the joint and brush with the marmalade mixture from one of the bowls to glaze and return to the oven.
- Serve the beef with roasted, new potatoes, parsnips, seasonal green vegetables, gravy and the untouched glaze from the second bowl.