Preheat oven to 400°F (200°C).
1. On baking sheet, combine turnips, 2 tbsp (25 mL) of the oil, ½ tsp (2 mL) of the salt and black pepper to taste; toss to coat evenly and spread in a single layer. Roast in preheated oven until turnips are tender and begin to color, about 20 minutes.
2. In a large pot, heat the remaining oil over medium-high heat. Add onion and sauté until softened, about 3 minutes. Add bok choy, garlic, five-spice powder and the remaining salt; sauté until bok choy is tender, about 5 minutes. Transfer bok choy to a plate and keep warm.
3. Add stock to the pot and bring to a boil. Add turnips, reduce heat and simmer until turnips have flavored the liquid, about 10 minutes.
4. Using an immersion blender, or in a food processor or blender in batches, pureé soup until smooth. Return to the pot, if necessary. Stir in cream, lemon juice, nutmeg and cayenne; reheat over medium heat, stirring often, until steaming. Do not let boil. Taste and adjust seasoning with salt and black pepper, if necessary.
5. Ladle into heated bowls and garnish with bok choy and chives.