Combine first 5 ingredients in a roasting pan or jelly-roll pan; toss well. Bake at 375° for 50 minutes or until tender, stirring occasionally. Cool 10 minutes.
Place half of squash mixture and half of broth in a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Place a clean towel over opening in blender lid (to avoid splatters). Blend until smooth. Pour into a large saucepan. Repeat procedure with remaining squash mixture and broth. Cook over medium heat 5 minutes or until thoroughly heated. Top with chives and pepper, if desired.