With the tip of a sharp knife, poke holes in the topside joint in various places. In each hole, insert a slice of garlic and sprinkle in some salt and pepper. Finally, season all over with a generous amount of salt and black pepper to taste.
Place the beef topside in a roasting tin. Pour in the beef stock and add the thyme and rosemary to the tin. Cover tightly with foil.
Cook in the preheated oven for 2 hours, or to taste depending on the degree of rareness liked. Uncover for the final 20 minutes of cooking to brown the top slightly. Rest at room temperature for 10 minutes, loosely tented with foil, before slicing.