Preheat oven to 400°F. Whisk together melted butter and brown sugar in a small bowl. Coat squash halves with butter mixture, reserving some of the butter mixture in bowl. Place squash, cut sides down, on a parchment paper–lined baking sheet. Bake in preheated oven until squash starts to turn golden on cut sides, 30 to 35 minutes. Flip squash, and spoon reserved butter mixture over squash. Return squash to oven, and continue baking until browned and caramelized, 15 to 20 minutes. Season evenly with salt and pepper. Place the acorn squash halves cut side down on the prepared pan. Roast for 30 minutes, flip the squash over and brush with juices from the pan. Continue roasting for about 20 minutes or until tender.