Preheat the oven to 375 degrees F.
Set the squash on its side and, with a large knife, cut in half vertically. Trim a piece off the bottom of each squash half so they will lie flat in the pan. Scrape out the seeds and stringy membranes with a large spoon. Place cavity side up in a large roasting pan.
Mix the butter, mustard, and honey in a small bowl until blended. Fill each squash cavity with 2 tablespoons of the butter mixture. Season with salt and pepper. Bake until the squash is very tender, 1 to 1 1/2 hours.
Note: Sandra Colling from Rochester, New York, called in one night on the show when I was making a dish with winter squash. She pointed out that anytime you have leftover cooked squash you can freeze it for future use. She suggested freezing it in muffin tins for easy single portions. I suggest that you could also turn the cooked squash puree into a soup by adding vegetable or chicken stock to thin, then topping it off with some homemade rye, pita, or Parmesan croutons.