How to Make It
Preheat the oven to 350°. Rub the cut side of the butternut squash with the olive oil and season with kosher salt and pepper. Set the squash cut side down on a baking sheet and roast for 45 minutes, or until very tender when pierced. Let the squash cool, then scoop the flesh into a bowl and mash lightly.
Meanwhile, in a large saucepan, combine the water, milk and table salt and bring to a boil. Gradually whisk in the cornmeal and bring to a simmer. Reduce the heat to low and cook, stirring every few minutes, until the cornmeal is smooth, about 30 minutes. Stir in the butter, Parmesan and mashed butternut squash. Season the polenta with kosher salt and pepper and serve hot.