Pre heat the oven to 180 degrees Celsius. Cut the top of garlic bulb. Don't peel it, keep it in tight structure. Put it in the middle of foil sheet. Poure top with olive oil and sprinkle it with salt. Wrap the foil tightly, shutting the garlic inside and put it to oven for 45 minutes.
Cut the onion in feathers. Melt the butter in pot. Add onion and thyme. Stir from time to time until onion is almost caramelized. Once garlic is baked move it aside to cool down. Once cooled, peel it or squeeze into the pot.
Peel and cut the potato into squares. Add them to the pot and pour in the stock. Let it cook until potatoes are soft.
When potatoes are soft, pour out a cup of the soup and leave it aside. Blend the soup, if it is too creamy use what you've poured out to dilute it. Add the sour cream and mix it.
Grate the cheese and mix it with flour. Add it carefully to the cream soup and mix on low heat trying to melt the cheese as much as possible. At the end bring it to boil. Add salt and pepper to taste.
Add croutons once poured into bowl.