01 - Heat vegetable broth in a medium saucepan and keep warm over low heat.
02 - Melt 2 tablespoons butter in a large heavy-bottomed skillet or Dutch oven over medium heat. Add chopped onion and cook until soft and translucent, about 3 minutes.
03 - Stir in minced garlic and cook for 1 minute. Add diced winter squash and cook, stirring occasionally, until it begins to soften, about 5 minutes.
04 - Add Arborio rice and chopped sage, stirring for 2 minutes until rice is well coated and slightly translucent.
05 - Pour in white wine and cook, stirring, until mostly absorbed.
06 - Add warm broth one ladleful at a time, stirring frequently. Allow each addition to be mostly absorbed before adding the next. Continue until rice is creamy, al dente, and squash is tender, approximately 20 to 25 minutes.
07 - Remove from heat. Stir in remaining 1 tablespoon butter, Parmesan cheese, and heavy cream if using. Season with salt and pepper to taste.
08 - Plate immediately, optionally garnishing with extra Parmesan and fresh sage.