Preheat oven to 375˚F.
Cut each squash in half across the grooves, scoop out the seeds and discard.
Cut about 1/2 inch off each of the bottoms of the squash halves and place them on a sheet pan. Season the insides with EVOO, salt, pepper and thyme. Roast 15-20 minutes, until pierced easily with a fork. Keep warm.
Meanwhile, boil the potatoes until tender, drain and reserve. Return the pot to the stovetop over medium heat. Add butter and bananas to the pot, and cook 5 minutes. Add reserved potatoes back to the pot along with the stock. Mash everything together until combined. Season with nutmeg, salt and pepper to taste.
Fill each of the roasted squash halves with the mashed sweet potatoes, top each with a sprinkle of amaretti cookies and serve.