Place the bacon in a small frypan with 1 tbsp olive oil. Cook over medium heat for 6-8 mins until the fat renders out and the bacon is caramelized. Drain the fat (but don’t discard) and set it aside. Place the stock in a small saucepan and bring to a simmer.
Meanwhile, place a large, deep frypan over medium heat. Add the reserved fat and the onion. Cook until softened. Add the rice and toss to coat with the oil. Add the white wine and cook, stirring, until reduced slightly.
Reduce the heat and gradually add the stock a ladleful at a time, while stirring gently. Keep adding the stock and stirring until the rice is cooked. This will take 15-20 mins. Turn off the heat, add the butter and parmesan and stir vigorously.
Add another ladleful of stock, the cavolo nero, and stir. Season to taste. Place the lid on and leave to rest for 1-2 mins, allowing the residual heat to wilt the leaves.
Serve in a shallow bowl, topped with freshly ground black pepper and crispy bacon.