Combine first 8 ingredients in a large bowl; stir well. Shape meat mixture into a 9 x 4-inch loaf on a broiler pan coated with cooking spray. Brush ketchup over meat loaf. Arrange potatoes around meat loaf on broiler pan.
Bake at 375° for 50 minutes. Let meat loaf stand 10 minutes before slicing. Split potatoes in half lengthwise; top with sour cream. Sprinkle with chives, if desired.
Note: To prepare the meat loaf in advance, shape the ground beef mixture into a loaf, wrap in heavy-duty plastic wrap, and freeze. Thaw overnight in refrigerator; bake as directed above.