An easy way to delight your guests. If you want extra vegetables, grilled or baked tomatoes are an excellent choice; we had tomates à la crème.
1 leg of lamb, about 2.5 kg
1 kg waxy potatoes (you can use more if you want some tasty leftovers)
1/2 litre chicken or vegetable stock (a cube is OK)
50 g butter at room temperature
4 cloves garlic
a few sprigs of rosemary
salt and pepper
Preheat the oven to 180C. Peel and thinly slice the potatoes, and chop the onion. Layer the potatoes in a large gratin dish, sprinkling with onion as you go, season with salt and pepper, and pour over the stock. Put in the oven on a low shelf to start cooking while you deal with the lamb.
Crush the garlic and mash together with the butter and broken-up rosemary leaves. Make six or seven slits all over the top surface of the lamb, and then use your hands to rub the butter mixture all over the surface, pushing it into the slits.
Place the lamb directly on an oven shelf above the potatoes. The garlic-laden juices will drip onto them as they cook. If the lamb is longer than the dish, you would be well advised to put a baking tray in the bottom of the oven to catch the drips and save cleaning.
Go away and have an aperitif with your guests. The lamb will take about an hour and a half to cook to medium rare, but check it before then. Leave to rest for 5-10 minutes before carving.