Separate the heads of garlic into cloves, but don't bother to peel them. Heat olive oil in a 2 litre pot over medium heat. Add garlic and cook, stirring occasionally for 15 to 20 minutes or until the skins turn golden. Add the onion and cook until soft, another 5 minutes. Add the broth, then the lemon juice, bay leaves and thyme. Increase heat to high and bring to a boil. Lower heat to medium and simmer for 30 minutes. Remove from heat, place contents of the pot in a food processor or blender and puree. Strain garlic puree through strainer into a medium pot over medium heat. Add milk cover, and bring to a boil. Immediatly reduce heat to low and simmer for 10 minutes. Serve hot.