Preheat the oven to 180°C (355°F). Place the sweet potato and oil on a baking tray and toss to coat. Cook for 25 minutes or until golden and tender. Set aside.
Heat a non-stick frying pan over medium heat. Add the extra oil and pancetta and cook for 2−3 minutes until crispy. Set aside.
Melt the butter in a non-stick frying pan over medium heat. Add the sage and cook for 1−2 minutes or until crispy. Set aside.
Place the rice and stock in a 22 x 30cm (8½ x 12 in) 10-cup (80 fl oz) capacity baking dish and stir to combine. Cover tightly with foil and cook for 40 minutes or until most of the stock is absorbed and the rice is al dente. Add the parmesan, salt, pepper, sweet potato and pancetta and stir to combine. Top with sage, drizzle with butter and serve immediately. Serves 4.