OR......
Pour some red wine around the joint before you put it in the oven. chuck in some sprigs of rosemary, some whole , peeled cloves of garlic (squashed) and a couple of red onions, peeled and sliced thinly. Cook your joint as normal, then, whilst it rests at the end of the cooking time, chuck the cooking juices and all the bits of garlic, onion and herb into a blender and whizz it up. You can thicken it a bit if you like, but it's not necessary. Really delicious. Oh, forgot to say - you will need to cook your roasties in another dish as they won't crisp up if you do them in with the meat using this method. Enjoy your dinner!