Melt butter in heavy large saucepan over medium-high heat. Add onions and thyme and cook until onions are translucent, about 6 minutes. Add roasted garlic and 18 raw garlic cloves and cook 3 minutes. Add chicken stock; cover and simmer until garlic is very tender, about 20 minutes. Working in batches, puree soup in blender until smooth. Return soup to saucepan; add cream and bring to simmer. Season with salt and pepper.
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