Heat a large heavy-based sauté pan with 1oz (2 tbsp) of the butter. Add the pumpkin with the sage and mix well to combine. Season to taste and cook over a gentle heat for 8-10 minutes, stirring occasionally until the pumpkin is cooked through but still holding its shape. Transfer to a plate and set aside.
Add 1oz (2 tbsp) of the butter to the pan and then tip in the onion and garlic and cook gently for 3-4 minutes until softened, stirring occasionally. Increase the heat, stir in the rice and cook gently for 1 minute, stirring continuously, until the rice is opaque and perfumed.
Meanwhile, pour the stock into a separate pan and bring to a gentle simmer. Add a ladleful of stock to the rice mixture and cook gently, stirring, until absorbed. Continue to add the stock a ladleful at a time, stirring frequently. Allow each stock addition to be almost completely absorbed before adding the next ladleful, until the rice is ‘al dente’ (tender with a slight bite). This should take 18 minutes but will depend on the type of rice you use.
Carefully fold the cooked pumpkin and sage into the risotto with the rest of the butter, the cheese and chives, then season to taste. Leave to rest and swell a little more for 3 minutes.
To serve, ladle the pumpkin and sage risotto into wide-rimmed warmed bowls and scatter with a little extra cheese and freshly ground black pepper. Garnish with the deep-fried sage leaves, if using.