Heat broth in medium sized saucepan and keep warm over low heat.
Heat Olive Oil in a large saucepan; add onion and butternut squash. Cook over medium heat until onion is translucent, about 5 minutes. Take care not to brown the squash too much.
Add rice to onion and squash. Cook 1 to 2 minutes. Add vinegar. Cook, stirring constantly until vinegar has been absorbed by the rice or evaporated. Add a few ladles of broth, just enough to barely cover rice. Cook over medium heat until broth has been absorbed. Continue cooking and stirring rice, adding a little bit of broth at a time, cooking and stirring until it is absorbed, until the rice is tender, but still firm to the bite, about 15 to 20 minutes.
Once all the broth has been absorbed and rice is al dente you can cover and set aside for about 5 minutes to rest.
Adjust seasoning and serve. To top, add about 1 tablespoon to each dish. Freshly grate a scant amount of nutmeg over the mascarpone and risotto.