1. Preheat the oven to 180°C.
  2. Line a baking tray with baking paper and place the sweet potato onto the tray, drizzle with 2 tbsp olive oil then sprinkle with nutmeg and sage leaves.
  3. Place into the oven and cook for 15 minutes or until soft and golden.
  4. Cook the pasta according to the packet directions, drain and set aside.
  5. Heat the remaining 2 tbsp olive oil in a frypan and gently sauté the garlic and leek until they soften.
  6. Add the cooked sweet potato and sage to the garlic and leek; season to taste.
  7. Toss through the cooked pasta and serve with grated parmesan.