This delightful twist on sweet potato casserole is sweet, warm, and comforting. If you're short on time, use Whole Foods' canned butternut squash purée instead of roasting your own. Marshmallows are optional, but recommended.
Preheat oven to 350°F. Place butternut squash halves, cut side down, on a baking sheet. Bake in preheated oven until tender when pierced with a fork, about 50 minutes. Let stand at room temperature until cool enough to handle, about 15 minutes. Scoop flesh from squash into a large bowl; mash with a potato masher, or puree in a food processor, until smooth. (Discard squash shell.)
Add eggs, brown sugar, heavy cream, melted butter, maple syrup, cornstarch, cinnamon, nutmeg, ginger, and salt to squash in bowl; stir until combined. Spoon mixture into a 13- x 9-inch baking dish coated with cooking spray. Bake, uncovered, at 350°F until set, about 40 minutes. Remove from oven; sprinkle with marshmallows.
Increase oven temperature to high broil. Return baking dish to oven; broil until marshmallows have browned, 2 to 3 minutes. Serve immediately.