Preheat the oven to 200°C (180°C fan-forced).
Line a baking tray with baking paper.
Combine the kumara and 2 tablespoons of the oil on the prepared tray; season with salt and pepper. Roast for 25 minutes or until tender. Reserve.
Add the remaining oil and bacon to the same oven tray; roast for 15 minutes or until crisp. Drain on paper towel, then crumble.
Bring the stock to a gentle simmer in a medium saucepan.
Melt the butter in a heavy-based pan over medium heat. Cook the onion, stirring, for 10 minutes or until soft. Add the rice and stir to coat.
Add the wine and stir constantly until the wine has been absorbed. Add ½ cup of the hot stock and stir constantly until the stock has been absorbed. Continue this process, adding ½ cup of stock at a time, stirring constantly, until the rice is tender and the risotto is creamy. This will take about 20 minutes.
Remove the risotto from the heat; stir in the roasted kumara, bacon and parmesan. Season to taste. Serve topped with reserved kumara, a drizzle of extra virgin olive oil and extra parmesan, if desired.
Suitable to freeze.