Heat oven to 350° Line a baking sheet with parchment.
Using a sharp knife, cut a thin slice from the blossom and stem ends to allow the halves to stand upright.
Cut each squash in half horizontally (see notes for the easiest way to do this)
Using a spoon, remove the seeds and stringy parts from each half.
Brush one tablespoon of olive oil over the cut end and the cavity of each squash half. Sprinkle with salt and pepper.
Remove the papery outer skin of the head of garlic and slice off the top. Place it on a square of foil large enough to wrap it in and drizzle it with the remainder of the olive oil. Wrap it up in the foil.
Put the squash halves cut side down on the prepared baking tray along with the foil wrapped garlic.
Roast 30 minutes or until the mashed potato squash can easily be pierced with a fork. Remove the squash but return the garlic to the oven for 10 minutes.
With a spoon, scoop out the flesh from each squash half into a bowl. Add the butter and squeeze the soft roasted garlic cloves from into the bowl.
Mash with a potato masher until creamy and fluffy.
Serve hot, garnished with parsley or fried sage leaves.
Notes
Trim the stem and blossom end off of the squash to make halving them easier and safer. Similarly, make sure you are using a very sharp chef’s knife.
Letting the garlic roast for a few minutes longer than the squash helps to achieve deep, rich, and caramelized flavors.
Store leftovers in an airtight container in the refrigerator for up to 3-4 days. Reheat them in a small saucepan or Dutch oven with the lid on over low heat, or in a covered bowl in the microwave.
Look for mashed potato squash with firm, smooth skin. Avoid those with soft spots or discolorations as these will go bad much more quickly.
For a unique spin, add herbs and spices such as rosemary, thyme, smoked or sweet paprika, chipotle, chives, or even horseradish.
For a nice presentation, reserve the shells and scoop the mashed squash back in to serve.