Preheat oven to 350 degrees F. Place the 26 cloves of garlic in small baking dish. Toss the garlic with 2 tablespoons olive oil and season with salt and pepper. Cover the baking dish tightly with foil and bake for about 45 or until garlic is soft and golden brown. Remove from oven and allow to cool enough to handle the garlic. Squeeze each garlic clove to release the garlic and place in a small bowl.
Heat a heavy bottom large saucepan over medium-high heat and melt 2 tablespoons butter. Saute the onions and thyme and cook until the onions are soft and translucent, about 6 minutes. Add the roasted garlic, 18 cloves of raw garlic and cook for an additional 3 minutes. Add chicken stock and cover and simmer for about 20 minutes or until the garlic is tender. Use an immersion blener to puree the soup until smooth or transfer in batches to a blender. Return the soup to the saucepan and add the heavy cream and bring to a simmer. Season with additional salt and pepper if needed.
Divide the grated Parmesan cheese equally into 4 bowls and ladle in soup. Squeeze lemon juice into each bowl and serve. Garnish with fresh thyme or chopped chives.