a la mode is a term that generally refers to ice cream that is served on top of pie or cake, mostly apple cake or apple pie
a la mode is a French term literally means "in the manner of" or "in the fashion of".
In American cookery it describes cake, pie, pudding or any other dessert topped with a scoop of ice cream. In French cooking it describes beef pot roast, larded with fat, braised with vegetables and simmered in a sauce. Example is Beef a la mode or Boeuf a la mode