Directions

1. Cut squash lengthwise, and scoop out the seeds and fibers. Cut each half into 4 pieces. Using a knife or mandoline, slice squash pieces 1/8 inch thick. Set aside.
2. In a medium, heavy-bottomed saucepan, heat oil over medium heat. Add onion, and cook, stirring, until soft, about 3 minutes. Add squash, season with salt, and add enough water to cover. Cook, simmering, until squash easily breaks apart, about 20 minutes. Stir in rice, then add a cup of broth. Bring to a boil, and cook, stirring often, for 8 minutes, adding one cup of broth at a time, as necessary; the rice should almost completely absorb the broth between additions.
3. Add cheese, stirring to incorporate, then continue cooking, adding broth as necessary, until rice is al dente and mixture moist but not watery, about 8 minutes more. Remove the pan from the heat. Stir in butter, and adjust the seasoning with salt, if necessary. Divide risotto between 6 serving plates, and drizzle with vinegar. Serve immediately.