Peel the butternut squash and cut it into bite-sized cubes. Toss with a drizzle of oil, season generously with salt and pepper, then spread out on a baking tray. Roast for 40 minutes, or until tender and lightly caramelised.
Slice the top from the garlic bulb to expose the cloves. Drizzle with a little oil, wrap in foil and roast for 30 minutes until soft and fragrant.
When the squash has been roasting for around 20 minutes, start the risotto. Add a splash of oil to a large frying pan or casserole dish over a low heat. Add the diced onion and cook gently for around 10 minutes, stirring occasionally, until soft, sweet and lightly caramelised.
Stir the risotto rice into the onions and cook for 5 minutes, allowing the grains to become lightly toasted.
Add a ladleful of hot stock and stir until absorbed. Continue adding the stock a little at a time, stirring regularly and allowing each addition to absorb before adding more. Keep going until the rice is tender with a slight bite in the centre. This should take around 20 to 25 minutes.
While the risotto cooks, prepare the crispy sage garnish. Heat a splash of oil and a knob of butter in a small frying pan until just beginning to smoke. Fry the sage leaves a few at a time for about 5 seconds per side. They should sizzle immediately and become crisp. Transfer to kitchen paper and sprinkle lightly with salt.
Once the squash and garlic are cooked, add half of the roasted squash to a bowl. Squeeze the softened garlic cloves from their skins and add them to the squash. Mash together with a fork until mostly smooth.
Stir the squash and garlic mixture into the risotto along with the crème fraîche, Parmesan and chopped sage. Mix well until creamy and luxurious. Season to taste with salt and freshly ground black pepper.
Spoon the creamy butternut sage risotto into bowls and top with the remaining roasted squash and crispy sage leaves before serving.