Prepare your acorn squashes by cutting each one in half and scooping out the seeds and pulp.
Place acorn squash halves skin-side down in a 4 quart or larger slow cooker.
With a sharp kitchen knife, score the flesh of the inside of the squash all over, being careful not to pierce the skin. This step will allow the butter and brown sugar to penetrate the flesh of the squash.
Evenly divide the butter and brown sugar between the two squash halves.
Cover and cook on HIGH for 3 hours or until the flesh of the squash is nice and tender.
Serve as is, or if desired, sprinkle with a pinch of salt or cinnamon.