Peel and cube the potatoes Place in a large bowl with the cold water Leave to one side Top and tail the leeks, then slice into chunks Wash in a bowl of cold water, drain and rinse Leave to drain in a colander Finely chop the onion Saute the garlic and onions in a large deep saucepan in the oil until tender. Add the potatoes and the water they have been sitting in. Increase the heat bringing the liquid to a rolling boil Add the yeast extract Stir well, reduce heat and add the leeks, black pepper, bay leaves and caraway seed. Stir well for 1-2 minutes Add the celery to the soup and simmer for a further 15 minutes. Serve hot.