Add olive oil and butter to a pot on low heat and add the onion. Sauté till translucent and grate in the garlic. Cook for 5 seconds.
Then add the potatoes, mushrooms, dried herbs, chilli flakes a little salt. Pour in a little of the broth, cover and cook on a low flame till the potatoes are cooked but not mushy (about 10 mins).
The add the chicken, the sausage (if using) and the remaining broth. Season again and simmer for 5 minutes till the soup comes together. Check the seasoning, add the pepper and turn off the flame. Serve with buttered, crusty bread.