Preheat oven to 350 degrees F
Spread the butter over the cut side of the acorn squash
Sprinkle some salt and pepper over the squash
Place the squash, cut side down onto a baking dish
Cook at 350 for 1 hour or until it is soft
While the squash is cooking, brown the ground beef.
Add the garlic, onions and mushrooms and cook until the onions are translucent
In a small bowl, beat the egg.
Add milk and 1/4 cup of cheese.
Add milk mixture to the beef mixture and mix well.
Add the arrowroot powder and seasonings and stir well.
Allow mixture to thicken for about 5 minutes
Stuff beef mixture into the cooked acorn squash
Top with remaining cheese
Bake for 30 minutes