Combine sugar and boiling water in a small bowl, stirring until sugar dissolves. Let cool. Add egg whites and baby food to cooled sugar mixture; stir until well-blended.
Combine flour and next 4 ingredients (flour through salt) in a medium bowl; stir well. Add egg white mixture to flour mixture, stirring until dry ingredients are moistened.
Pour batter into a 9-inch square baking pan coated with cooking spray. Bake at 350° for 40 minutes or until cake springs back when touched lightly in center. Let cool completely in pan on a wire rack. Sift powdered sugar over top of cake.