Preheat oven to 400 F.
Cut squash in half, lengthwise and place flesh side up in a glass baking dish (9x13 inch). Add water and place uncovered in oven. Steam-roast for 45 to 60 minutes or until all flesh is tender.
While squash is cooking, put olive oil, white sugar and balsamic vinegar into a small skillet; add onion slices and cook on medium heat for five minutes. Turn heat to low/simmer and cook for another 30 minutes, stirring occasionally. Once the onion mixture is caramelized, combine with celery.
Scoop out the flesh of the cooked squash and mix with butter, brown sugar and cinnamon. Place the squash mixture into a serving dish, adding the caramelized onion and celery mixture over the top.
Do you have a favorite way to prepare butternut squash in the fall? If so, I hope youll share it with me.