Start by peeling the squash but don't worry about the skin in the crevices. Trim the ends and then cut the squash in half lengthwise. You'll need a big knife to cut through the squash so be careful.
Scoop out the seeds with a spoon and then cut the squash crosswise into ½ thick pieces.
In a large fry pan, skillet or saute pan, heat one tablespoon of olive oil over medium-high heat. So not to overcrowd the pan, cook half of the squash pieces in a single layer making sure not to move them until the slices begin to brown. This should take about two minutes.
Flip the squash over and cook on the other side until they begin to turn brown. Again they should take about two minutes.
Transfer the squash to a baking dish that has a cover or use foil if you don't have one. Finish cooking the rest of the squash and transfer to the baking dish trying to keep everything in a single layer.
Sprinkle about two tablespoons of the sherry along with half a teaspoon of salt and a little bit of the ground pepper on top of the squash.
In the same pan, heat the other tablespoon of olive oil and butter over medium heat. Add the shallots and a little bit of salt and cook until the shallots turn a golden brown. This takes 3-5 minutes but be sure to stir often.
When the shallots are done remove the pan from the heat and add the sage along with the remaining two tablespoons of sherry. Use the sherry to deglaze the bottom of the pan while scraping any browned bits stuck to the bottom of the pan. Place the shallots over the squash in the baking dish.
Cover the pan and bake until squash is fork tender which should take about 30 minutes.