"To set the chocolate" means to allow the chocolate to become firm or solid. It involves cooling or refrigerating the melted chocolate until it hardens and becomes stable. Full definition
First you break through the perfectly set chocolate shell, and you get to the sweet, soft date. (beamingbanana.com)
Or you can set your chocolate covered walnuts on a piece of wax paper and firm up in the freezer to serve on top of your ice cream. (forestandfauna.com)
I really believe that is one of the things that sets my chocolate chip cookies apart from others. (bakingandboys.com)