Preheat the oven to 450ºF.
Halve the squash lengthwise and scoop out the seeds.
Lightly oil a shallow baking dish and place half of the squash, cut side down, in the baking dish. Peel the other half of the squash then dice it into 1/4-inch cubes. Add the diced squash to the baking dish, scattering the cubes around the sides of the halved squash.
Bake the squash, stirring the cubes occasionally, for 15 to 20 minutes.
Remove the squash from the oven. Transfer the cubed squash to a bowl, and holding the halved squash in a kitchen towel, scoop out the flesh and roughly chop it. Transfer the chopped squash to the bowl with the cubed squash.
Combine the chicken broth and water in a medium saucepot over medium-low heat. Bring it to barely a simmer.
Add the butter to a separate large saucepot over medium-low heat, then add the onion and garlic and sauté until soft, about 3 minutes.
Increase the heat to medium and stir in the rice. Add the wine and continue cooking, stirring until the wine is absorbed. Stir in 1/2 cup of the barely simmering chicken broth, and cook at a simmer, stirring constantly, until broth is all absorbed. Continue simmering and adding broth, about 1/2 cup at a time, stirring constantly and allowing each addition of broth to be absorbed before adding more until half the broth has been added.
Stir in all of the roasted squash and continue simmering and adding broth 1/2 cup at a time until the rice is tender and creamy but still al dente, about 18 minutes.
Stir in 1/3 cup grated Parmesan cheese and 2 tablespoons chives. Season with salt and pepper to taste and serve the risotto, garnished with additional Parmesan and chives.
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