Melt butter in a large saucepan over medium heat.  Add onion and cook until softened and translucent (reduce heat if browning).  Add garlic and ginger, cook a minute more. Add remaining ingredients, cover, and bring to a boil, then reduce to a simmer and cook until carrot and apple are very tender, about 25 minutes.

Transfer soup to a standing blender and puree (do it carefully in batches unless your blender is designed for hot liquids!), or use an immersion blender.  Taste and add more salt if needed.  Garnish bowls with chopped parsley, freshly ground pepper, and/or sumac, as desired.