Fennel and Carrot Soup

Melt butter in a heavy pot over medium heat. Add fennel, carrots, celery, leeks, thyme, and bay leaf. Season with salt and pepper. Reduce heat to medium-low. Cover and cook, stirring occasionally, until vegetables soften but do not brown, 30 to 45 minutes.

Pour broth into the pot and bring to a boil. Reduce heat and simmer until all of the vegetables are cooked, about 10 minutes. Remove the thyme stems and bay leaf. Puree soup using an immersion blender.