Preheat the oven to 425 degrees.
On a large and heavy baking sheet lined with parchment paper, place the butternut squash and drizzle with olive oil. Toss to coat and arrange each slice of squash flat on the baking sheet so it gets well caramelized. Sprinkle with salt and pepper.
Place in the oven for 30 minutes.
Remove the baking sheet from the oven and dot the butternut squash with the butter cubes.
Then scatter the sage over the squash and place the baking sheet back in the oven for 15-20 minutes, or until the squash is equally tender and golden.
When the squash is done, season again with a little more salt and pepper and serve immediately.