Cook macaroni in boiling water according to pack instructions. Drain, rinse well.
Melt butter in a small saucepan. Remove from heat and stir in flour. Gradually stir in milk. Return to a medium heat and stir constantly until boiling. Lower heat and simmer for 2-3 minutes, stirring occasionally.
Stir PediaSure Complete® and cheese into sauce. Mix macaroni with sauce and pour into a lightly greased 2-cup capacity oven proof dish.
Combine breadcrumbs and extra grated tasty cheese, sprinkle over macaroni. Bake at 200˚C for 5-10 minutes, until golden brown and hot.