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Preheat oven to 400 degrees F.
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Cut squash in half and scrape out seeds. Discard seeds or roast them separately as you would with pumpkin seeds.
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Slice squash into 1-inch strips. Drizzle 1 tablespoon olive oil over the squash and toss to coat. Place the squash strips on a baking sheet and roast until tender, about 30 minutes.
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While the squash is roasting, heat remaining 1 tablespoon olive oil and 1 tablespoon butter in a heavy bottom saucepan over medium heat.
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Add onion and cook until softened and opaque, stirring occasionally. Add garlic and allspice, stir, and cook until fragrant (about 1 minute).
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Add rice and stir to combine. Continue stirring and cooking until the edges of the rice are translucent and the center is still opaque, about 2 minutes.
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Add wine and stir to combine. Cook until the rice absorbs the wine, stirring occasionally.
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Add warm broth, a ladle at a time, stirring after each addition and occasionally stirring while cooking. Wait to add each ladle of broth until the rice has almost soaked up the last addition.
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Test the rice after you have added about 3 cups of broth to see if it is done. It should be al dente, with just a bit of chew to it and not completely soft or mushy.
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Note the risotto will not taste fully seasoned at this point. It will get saltiness from the parmesan cheese.
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The risotto is ready when it is similar to a thick porridge and have a creamy consistency.
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Add one more ladle of broth, remaining 2 tablespoons butter, and parmesan cheese. Stir to combine.
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Cut the roasted squash into bite-sized chunks and gently stir into the risotto. Serve immediately.