Cut the squash in half lengthwise and scoop out all of the seeds with a spoon.
Place the squash cut side up on a lined baking sheet. Drizzle with olive oil and sprinkle with salt and black pepper.
Roast in the oven until fork tender, approximately 40 minutes. Remove from the oven and set aside.
In a medium or large pot, combine the butter, vegetable stock, sage, salt, black pepper, and garlic powder. Simmer over medium heat for 5 minutes to incorporate flavors. Remove pot from heat.
Scoop the butternut squash out of the skin shells and put in the stock mixture.
Using a masher, mash the squash into the liquid.
Season to taste as desired. Serve warm.
This can easily be kept warm in a slow cooker or in a baking dish, covered, on warm in the oven.Want a faster cook time or a deeper roasted flavor? Peel and cut the squash into cubes before tossing and roasting in the oven.Want it extra creamy? Add more stock or butter as desired.