Combine olive oil and onion in a medium saucepan and cook over medium heat until onion is tender.
Meanwhile, dice turnips, potato, and apple into 1" cubes.
Add all ingredients except cream to the saucepan. Bring to a boil, reduce heat to simmer and cook covered 12-14 minutes or until all vegetables are very tender.
Using a hand blender or a regular blender*, blend until smooth (see notes for regular blender).
Stir in cream and heat through for 2-3 minutes.
Garnish with herbs and croutons if desired.
