Add the olive oil and onion to a large saucepan and cook over a medium heat for 2-3 minutes, until the onion begins to soften. Add the carrot and celery and cook for 4-5 minutes, then add the pancetta. Season and stir well, cooking for 2 minutes until the pancetta becomes crispy. Add the garlic and rosemary, cooking for another 1 minute.
Break in the mince using a wooden spoon and brown all over for about 3-4 minutes. Add the chicken livers and stir well to combine, then add a pinch of the grated nutmeg.
Pour in the wine and allow to reduce for 1 minute, before pouring in the chopped tomatoes. Bring to the boil, cover and simmer gently for 60-75 minutes, topping up with more liquid if needed. Remove the lid for the last 15 minutes so the sauce thickens.
Meanwhile, cook the spaghetti according to the instructions on the packet. Drain and divide between four plates. Spoon over the bolognese and serve sprinkled with parmesan and fresh basil leaves.