Use a large knife to cut stem off squash and then to cut it in half vertically. Use a spoon to scrape out seeds and any stringy stuff from inside the squash. Set squash on a baking pan, cavity side up. If it wobbles too much, slice a piece off the backside so squash will lie still and flat.
Combine butter, mustard and honey and place into cavity of squash. Top with a light sprinkling of salt and pepper.
Bake until squash is very tender, about 1 to 1-1/2 hours.
For a variation on sweetness, use 2 tablespoons of real maple syrup instead of honey.