To peel the garlic, separate the cloves and drop them into boiling water for 30 seconds, drain, rinse the cloves in cold water, then peel them. Saute the sliced leeks in the oil until tender, then put them and all the rest of the ingredients into a soup pot and bring the mixture to a boil. Reduce the heat and simmer for 35 to 45 minutes, or until the garlic is tender and dissolving. Fish out the cooked potatoes, whip them until smooth, then reserve them. Strain the soup through a sieve, pressing to get all the garlicky goodness into the strained soup. Add the reserved potatoes, and whisk them in until smooth.