Heat your oven to 200°C/Fan 180°C/Gas 6. Halve the squash. Scoop out the seeds. Peel and chop the squash into 2 cm cubes. Chuck them in a roasting tin. Drizzle with 1 tbsp oil. Season. Roast for 30 mins till soft. Turn the oven down low to keep it warm.
Meanwhile, peel and finely chop the onion. Trim and coarsely grate the courgette. Peel and crush the garlic.
Crumble the stock cube into a measuring jug. Pour in 750ml boiling water and stir to dissolve the stock cube.
Melt the butter in a pan over a medium heat. Add the onion and season. Fry for around 5 mins till the onion is glossy and soft. If the onion starts to brown, turn down the heat. Stir in the garlic.
Add the grated courgette to the pan. Stir well and fry for 2-3 mins till the courgette is soft. Stir in the risotto rice. Pour in a splash of the hot stock. Stir and cook over a medium heat till the rice has absorbed the stock.
Add another splash of the stock and stir till it has all been absorbed. Continue this way for 20-30 mins till you’ve used all the stock. The risotto will look creamy and the rice will be soft but still have bite.
Taste the risotto. Add salt and pepper if you think it needs it. Finely chop the sage leaves. Stir most of them into the risotto. Serve the risotto in warm bowls topped with the roast squash and remaining sage leaves.