Place frozen butternut squash, chicken stock and water into a large pot. Bring to a boil and then reduce to a simmer.
In a large pot or braiser over medium heat, place the olive oil, chopped onion, salt, and sugar until the onions start to caramelize. Add the rice to the pot and let it absorb the oil while stirring for about 3 minutes. Add the white wine and stir until incorporated.
Add the butternut squash/chicken stock mixture to the rice three ladles full at a time. Cover and let the rice absorb, about 2-3 minutes. After the rice has absorbed the liquid, repeat the previous step until the squash/broth mixture has all been used. This should take approximately 10-15 minutes.
Once finished and the rice is smooth and creamy, take off the heat and add in the rosemary and butter. Once the butter has melted, mix in the parmesan and stir.