Cut the onion into small pieces and sauté in olive oil.
In the meantime, peel the carrots and cut into small pieces. Add to the onions and sauté for five minutes, then pour the stock over and simmer for 10-15 minutes.
Puree with a hand blender until the soup has the desired consistency. I like it rather thick, if you prefer it thinner, just add some broth.
Season with salt, pepper and chilli flakes and pour finely crumbled feta on top.
Tip: The soup also tastes delicious with a little orange juice or cream.