01 - Melt butter in a large pot over medium heat. Add onion, carrot, and celery. Sauté for 5 minutes until softened.
02 - Stir in minced garlic and cook for 1 minute until fragrant, being careful not to burn it.
03 - Add diced potatoes, thyme, nutmeg, vegetable stock, salt, and pepper. Bring to a boil, then reduce heat and simmer covered for 20-25 minutes until potatoes are tender when pierced with a fork.
04 - Use an immersion blender to puree the soup until completely smooth. Alternatively, leave some chunks for a rustic texture if preferred.
05 - Stir in whole milk, heavy cream, grated cheddar cheese, and sour cream. Cook over low heat for approximately 5 minutes, stirring constantly until cheese is fully melted and soup is creamy. Adjust seasoning with salt and pepper as needed.
06 - Ladle hot soup into serving bowls. Top generously with additional grated cheddar cheese and chopped fresh chives. Serve immediately while hot.