Place one oven rack low enough to accommodate your pot with the lid on. This is probably the lowest or 2nd lowest position in your oven. Place the other rack in the top position. We will bake the risotto on the lowest rack and roast the squash on the upper rack.
Preheat oven to 400°F
While the oven heats, line a baking sheet with parchment paper. Prepare the squash and arrange it in a single layer on the parchment-lined baking pan.
When the oven comes to temperature, put the squash in the oven on the top rack. Allow it to roast at 400° while you perform the next steps.
While the squash is roasting, heat the large oven-safe pot to mercury ball temperature. See the video link for an explanation. https://www.youtube.com/watch?v=CB-SCA1reqE
When the pot is ready, add diced onion and a pinch of salt. Saute on medium heat until fragrant and translucent, about 5 minutes. Add minced garlic and saute till fragrant, about 1 or 2 minutes. Do not allow garlic to burn. Add a splash of water or broth if the onions or garlic start to stick or burn during sauteing.
When the onion-garlic mixture is fragrant, mix in 3 cups of broth and 1 cup water. Cover the pot and bring to a boil over medium-high heat. When it is boiling, stir in the rice and replace the lid. Set and allow the rice-onion-garlic to boil for 15 minutes.
After 15 minutes, remove the pot from the stovetop and place it in the hot oven on the lowest rack. Decrease oven temperature to 375°. Bake until rice is cooked, about 50-60-ish minutes. Test both squash and rice for doneness after about 40 minutes. The rice is "done" when the rice is soft but chewy. It will also seem pretty dry, but we will fix that directly!
Meanwhile, the squash is "done" when it is fork-tender, and edges are caramelized. When it is ready, remove it from the oven and set aside.
When the rice is done (soft but chewy), carefully remove the covered pot from the oven. Caution! The whole thing will be SCREAMING hot! Place the pot on a heat-safe surface and remove the lid. Stir in 1/2 cup of vegetable broth. Avoid splashing.
While the squash and rice are baking, you can saute the sage leaves in a non-stick skillet. Pan fry the leaves till they turn a darker green. Do not let them turn brown! Then remove them from skillet and set aside.
This is the home stretch now: Take 1 cup of the cooked rice, ½ cup squash, and the remaining ½ cup broth and put in blender or food processor. Puree till smooth.
Return pureed mixture to the pot of cooked rice. Add wine or sherry, 1½ Tbs nutritional yeast, and stir vigorously to distribute evenly throughout. The risotto should look pretty creamy at this point. Stir in roasted squash. Add salt, pepper, and red pepper flakes and adjust to taste. Stir well to combine.
Serve as desired with crushed sage leaves sprinkled on top. Yummmmm!