Preheat the oven to 190°C/170°C fan. Place the pumpkin cubes and half-moons on a baking tray, drizzle with a little olive oil, season, and roast for 30 minutes until tender. Set the half-moons aside for serving.
In a large, deep frying pan over medium heat, fry the pancetta cubes until crisp, about 10 minutes. Remove with a slotted spoon and set aside, leaving the fat in the pan.
Add 1 tbsp olive oil to the same pan with the pancetta fat. Once melted, stir in the onion and cook over a medium heat for about 7 minutes until softened. Add the garlic and cook for 30 seconds, then stir in the rice. Cook for 1–2 minutes, coating the grains in the buttery onions.
Pour in a ladle of hot stock and stir constantly until absorbed. Continue adding stock, one ladle at a time, stirring often, until the rice is just cooked and creamy (18–22 minutes).
Blitz the roasted pumpkin cubes (not the half-moons) with the double cream until smooth, adding a splash of stock if needed. Season well.
Stir the blended pumpkin, Parmesan, butter, and crispy pancetta into the risotto. Season to taste.
Spoon the risotto into bowls and top with the roasted pumpkin half-moons, fried sage leaves, and a little more Parmesan. For extra richness, melt a knob of butter with chopped herbs and drizzle over the top.