Peel and chop all veggies before you begin; set aside.
In a large heavy-bottomed pot, melt the butter over medium heat. Add onion and cook until translucent, about 5 minutes. Add potatoes and carrots and cook 5 minutes more. Add garlic, and cook 1 more minute.
Add stock and bring to a boil. Stir in cauliflower, cover, and reduce heat to a simmer. Let cook until vegetables are tender, 15-20 minutes.
Puree using an immersion blender or in batches in the blender. Return pureed soup to pot over low heat, and stir in the cream, Parmesan cheese, and 1 teaspoon of thyme. Season soup with salt and pepper to taste.
Ladle soup into bowls, sprinkle with additional thyme and garnish with croutons, if using. Enjoy!
Additional Toppings: Roasted cauliflower florets, roasted chickpeas, crispy bacon, cheddar cheese or green onions.