Saw the first title listed in Publishers Weekly (I spent some time today going through the stack of magazines, which included 4 PWs), then decided to Google "chocolate novels."
Daalder's Chocolates by Philibert Schogt, trans. from the Dutch by Sherry Marx, Thunder's Mouth, 10/05.
Dying for Chocolate by Diane Mott Davidson, 1993.
Chocolate Chip Cookie Murder by Joanne Fluke, 2001.
Chocolat by Joanne Harris, 2000.
Sweet and Low by Emma Lathen, 1983. Includes chocolate.
The Big Bad City by Ed McBain, 1999. Includes chocolate chip cookies.
Such Devoted Sisters by Eileen Goudge, 1992. Includes chocolate.
Poirot Investigates The Chocolate Box by Agatha Christie, 1925.
A list of chocolate and related titles from the Morton Grove Public Library, 2001.
And a few more here from the Omaha Public Library.