Thoroughly rinse lettuce and remove cores. Heat a soup tureen. Place lettuce leaves in a large, dry saucepan and cook over medium heat for 6 minutes. Into another pan on low heat, place butter, stir in onion, and let cook until soft. Stir in flour, making a roux. Cook 3 minutes while stirring. Stir milk into roux and half of the chicken stock. Remove cooked lettuce from pot, puree in a blender and add to soup. Add rest of chicken stock and cook while stirring for 7 minutes or until thickened. Season to taste with salt and pepper. Pour 4 tb clarified butter into a small frypan and when heated, add cubes of bread, occassionally shaking pan to prevent them from getting too brown. Add another 2 tb clarified butter and garlic cloves. Drain garlic bread "croutons" on a paper towel. Place on heated serving dish. Strain lettuce soup through a sieve into soup tureen and serve at once with croutons.