Preheat the oven to 200℃ (390℉).
Scatter the diced butternut squash onto a lined baking tray and drizzle with olive oil. Shake the pan to coat. Roast for 30 minutes or until the butternut has softened and is starting to caramelise. Set aside to cool. Reserve ¼ of the butternut for serving.
Place a medium sized saucepan or pot (I like to use a cast iron casserole pot) on a medium-high heat. Once the pan is hot, add a drizzle on olive oil to coat the bottom of the pan. Sprinkle in the sage leaves and fry for a minute until crispy. Remove with a slotted spoon and place on a paper towel.
Turn the heat down to medium and add the diced shallots with 1 tbsp butter. Sauté until softened.
Reserve ½ of the stock for the butternut puree. Place the remaining stock in a separate saucepan on medium heat until just simmering. Keep on a low gentle heat.
For the butternut puree, add the roasted butternut cubes to a food processor (reserve a quarter for serving). Add the reserved ½ cup stock and puree until smooth. Season to taste.
Add the arborio rice to the shallots and stir to coat all the grains. Sauté for a minute or two whilst stirring to lightly toast the rice.
Turn to heat down to medium-low and add the white wine. Stir until at least half the liquid has reduced.
Add the stock one ladle at a time, stirring between additions. Continue until the rice is al dente with a creamy consistency. You may not need to add all the stock.
Remove the risotto from the heat. Add the butternut puree along with the remaining butter and the grated parmesan and stir briefly to combine. Cover with a lid and let stand for 10 minutes before serving. Season to taste after resting.
Serve with the remaining roasted butternut, scatter over the crispy sage leaves and tear over pieces of prosciutto.