1. Heat the oil in a large saucepan over medium heat. Add the onion and ginger and cook, stirring occasionally, until soft and fragrant, about 5 minutes.

2. Add the carrots, stock, and orange juice. Increase the heat to medium-high and bring to a boil. Reduce the heat to low, cover the pan, and let simmer until the carrots are very tender, about 45 minutes.

3. Using an immersion blender, puree the soup in the saucepan. (Or, let the soup cool slightly, then puree it in a blender or food processor.) If you prefer a smoother texture, strain the pureed soup through a sieve.

4. Add the nutmeg to the soup and season it with salt and pepper to taste. If the soup is too thick, thin it with some water or more stock.

5. To serve the soup warm, reheat it gently over medium-low heat. To serve the soup chilled, refrigerate it, covered, until cold, at least 6 hours or up to 5 days. Garnish the soup with a spoonful of crème fraîche and a light sprinkle of nutmeg before serving. If desired, you can create a swirl pattern in the soup by dragging the tip of a knife or fork through the crème fraîche in a circular motion.