Preheat the oven to 425 degrees F. Cut the squash into wedges, slices, or cubes and arrange them on a rimmed baking sheet. Drizzle them with olive oil, sprinkle them with salt, and arrange some fresh thyme leaves around the squash. Roast for 25-40 minutes, until the squash is tender.
While the squash cooks, place your risotto pot on the stove. Heat 1 tablespoon of olive oil over medium high heat. Add the chopped onion and sliced leeks and cook, stirring regularly, until the wilt and brown a little.
Add the greens and stir them into the onions and leeks. Cook until tender.
Add the butter and the rice and stir to combine. Cook for 1-2 minutes, until all the rice grains are glistening and separated.
Pour in the white wine and stir to combine until it's been absorbed.
Once the wine has absorbed, add just enough stock to cover the rice and veg, and stir until it's been incorporated.
Continue adding the stock and stirring, until all the stock as been absorbed.
When you've incorporated all the stock, remove the pot from the heat. Stir in the parmesan cheese and heavy cream. Taste and add some salt and pepper to taste.
Cut about half the squash away from the peels and into chunks. Stir it into the finished risotto. Reserve about half the roasted squash to use as a garnish. Serve hot.