Heat oven to 350°F. Grease bottom only of 9x5-inch loaf pan with shortening or cooking spray.
In large bowl, mix butter, granulated sugar, eggs and pumpkin with wire whisk. Stir in flour, baking soda, cinnamon and pumpkin pie spice. Stir in chocolate chips and walnuts. Spread in pan.
Bake 55 to 65 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes; remove from pan to cooling rack. Cool completely, about 2 hours.
If you decide to add the glaze: In small bowl, stir powdered sugar and milk until smooth and thin enough to drizzle. Drizzle over loaf. Let glaze set up before slicing, about 30 minutes.