Heat the butter and oil in a large, heavy pot or Dutch oven over medium heat. Add the fennel, onion, carrots, potato, thyme and bay leaf. Season with salt and pepper. Reduce heat to medium-low, cover and cook. Stir the vegetables occasionally and reduce heat if needed. Cook the vegetables until they’re soft, but not browned and have released their moisture, about 30-45 minutes (this is called sweating the vegetables).

Add the broth, bring to a boil and season with salt and pepper as needed. Reduce heat and simmer until the potatoes are falling apart, about 8-10 minutes. Let cool slightly and remove the herbs. Puree the soup in batches in a blender or with an immersion blender, until smooth. Optional- strain the soup through a fine mesh sieve or strainer, for a smooth soup.

Mix creme fraiche and maple syrup in a small bowl. Serve soup topped with the maple crème fraiche and a drizzle of olive oil.