In a large bowl, cream butter and sugar. Add eggs, one at a time, beating well after each addition. Add pumpkin and vanilla; mix well. Combine the dry ingredients. Stir into pumpkin mixture just until moistened. Fold in chocolate chips and walnuts.
Spoon into two greased 8x4-in. loaf pans. Bake at 350° for 65-75 minutes or until a toothpick inserted in the center comes out clean. Cool for 10 minutes before removing from pans to wire racks. If desired, combine glaze ingredients; drizzle over cooled loaves.