Grease 9″x9″ pan. Spread cornflakes in pan. (Try not to go to the edge, as this will make it easier to remove the hardened candy with a spatula.)
Heat sugar and margarine to boiling in saucepan, stirring constantly for 7 minutes.
Immediately spread on top of cornflakes. Sprinkle chocolate chips over hot mixture, and place cookie sheet over pan until the chocolate is melted. Spread the melted chocolate over the candy.
Cut into squares while hot. (Chocolate will still be soft – set bars aside, separated by wax paper.)
Refrigerate til firm.