Turn Carnival squash upside down onto a cookie sheet. Bake in a 350 degrees F (175 degrees C) oven until it begins to soften, approximately 30 to 45 minutes.
Remove squash from the oven and turn onto a plate so that the flesh is facing upwards. Place butter and brown sugar into the squash, and place remaining squash over the other piece. Place squash in a baking dish (so the squash wont slide around too much) while baking.
Place squash in the 350 degrees F (175 degrees C) oven and bake another 30 minutes.