Corned beef sandwiches were prepared by Molly Weasley for the journey to Hogwarts on the Hogwarts Express. Ron Weasley was not particularly fond of these sandwiches, but his mother never seemed to remember that point. However during his third year at Hogwarts, when she was handing out the sandwiches, Ron pulled a face and she told him that in fact no, they weren't corned beef.