Melt 2 Tablespoons butter in a heavy, large saucepan over medium-high heat.
Add 2 onions and 2 teaspoons thyme and cook until onions are translucent, about 5 minutes.
Add roasted garlic and 18 raw garlic cloves and cook a couple of minutes to release some of the raw garlic oils.
If you're adding the russet potato chunks, add now as well.
Add 4 cups chicken or vegetable broth; cover and simmer until garlic is very tender, about 20 minutes. If you're making the Parmesan Cheese Crisps, make them now while the soup is simmering.
If you added the russet potato chunks, remove them after the 20 minute simmer and place in a small bowl or on a plate while you puree the rest of the ingredients. Working in batches, puree soup in a blender until smooth or puree with an immersion blender. Return potato chunks to the creamed soup.
Return soup to the saucepan, add ½ cup cream, or whatever milk you are using, and bring to a very low simmer just to reheat, being careful not to curdle the milk. Add ½ teaspoon salt and ½ teaspoon freshly ground pepper. Taste and add more to your liking.
Divide the grated ½ cup of Parmesan cheese among 4 bowls and ladle soup over. Each bowl will get about 2 tablespoons of cheese.
Squeeze juice of 1 lemon wedge into each bowl and serve.
Serve in individual bowls garnished with more grated Parmesan, Parmesan Crips or toasted croutons, or the additional minced sauteed garlic.