Wash the meat and dab dry. Peel garlic cloves and press 3 cloves through a garlic press. Wash oregano, dab dry and pluck the leaves from the stalk. Pluck rosemary needles from the stem.
Mix herbs, except for a little bit for garnishing, wine, lemon juice, crushed garlic, oil, salt, pepper, juniper berries and 3/8 litres of water. Place the leg of lamb in a bowl and pour the marinade over it.
Put the marinated leg of lamb in a cool place for about 3 hours. Cut the remaining garlic into slices. Remove the leg of lamb from the marinade, place on a fat pan and roast in a preheated oven (electric range: 175°C/ gas: level 2) for approx. 2 1/2 hours.
After about 1 hour, pour half of the marinade over the roast. Add the rest of the marinade bit by bit to the roast. Put garlic slices on the roast 1/2 hour before the end of the frying time. In the meantime, clean, wash, peel and dice the turnip.
Cook with the beans in boiling salted water for about 15 minutes. Melt the sugar in a dry pan and add 3/8 litres of boiling water while stirring. Season with salt and pepper. Add rutabaga and beans to the pan and caramelise for about 5 minutes.
Remove the roast from the oven and cover and keep warm. Pour marinade through a sieve into a pot, bring to the boil and add sauce thickener. Bring to the boil again and season to taste with salt and pepper.
Arrange roast and vegetables on a plate and serve garnished with rosemary and oregano. Serve with extra sauce.