Preheat the oven to 200°C (400°F/Gas 6). Cut the whole orange and lemon into quarters lengthways (or into 6 wedges, if they are large) and put to one side. Keep the halves for later.
Put the oil and butter in a flameproof roasting tin and put over medium heat until the butter melts. Add the veal, garlic, shallots and carrots, turn the heat to high and brown the meat, salting and peppering the done sides and turning the vegetables over when you turn the meat.
Add the rosemary and thyme and put the tin in the oven. Roast for about 20 minutes, or until the surface of the veal looks bubbling and golden, then turn it over. Squeeze in the juice from the orange and lemon halves, and add the wine. Roast for 10 minutes, then add the orange and lemon wedges. Reduce the temperature to 180°C (350°F/Gas 4) and roast for another 10 minutes. Turn the wedges, taking care not to pierce them and ruin their shape, then roast for a final 20 minutes. Remove from the oven and let the dish sit for about 15 minutes.
Remove the string before carving the meat into fine slices. Serve with the pan juices, some carrots and an orange and lemon wedge for each person.