Put the duck breasts in a shallow dish and pour over the Port, balsamic vinegar, olive oil, orange juice and add the thyme leaves. Add plenty of freshly ground pepper. Mix well then marinate in the fridge for about 4 hours.
Take the meat out of the fridge 30 minutes before cooking.
Heat a griddle pan or barbecue or set the grill to medium in the oven. Season the duck with salt, then grill the skin first, then turn over and cook the flesh. Keep brushing the meat with the marinade.
The cooking time depends on the thickness of the breasts and how well-cooked you like duck. Ideally it should be pink, bit if you prefer it cooked “properly” , make sure you don’t overcook it as duck can become very chewy.
Rest for 5 minutes before serving.
Serve it with the cooking jus or balsamic glaze.