Put butter, icing sugar, flour, corn flour in bowl. Mix with wooden spoon- do not beat with electric mixer. Or use paddle attachment.
Put in piping bag with a nozzle attachment (star). Pipe onto non stick baking sheet.
Bake for 15min until golden brown.
Once cooled, melt chocolate (the methods of doing so- microwave, set over hot water, simmer over hot water). Dip half of the cookie into chocolate.
Let it sit until cooled and set