Preheat oven to 400 degrees and line a baking sheet with foil.
In a large bowl, toss butternut squash cubes with olive oil, sage, red pepper flakes, and salt.
Spread the squash on prepared baking sheet and roast for 40 minutes minutes, tossing once halfway through cooking time. Remove from oven and let cool slightly.
When squash has cooled a bit, put in in a blender or food processor and add milk, water, and parmesan cheese and blend until smooth.