In a medium saucepan over low heat, combine the milk, cocoa, and sugar. Bring it to a simmer until the mixture thickens slightly.
Remove from heat and whisk in the eggs one by one.
Add the salt, then slowly pour in the melted butter while stirring constantly. Return pan to stovetop and continue cooking over medium heat until the custard reaches 160 degrees Fahrenheit on a candy thermometer. Strain through cheesecloth into a metal bowl placed inside another larger bowl filled with ice water. Stir occasionally until cooled completely, about 30 minutes.
To serve, fill a large glass serving dish with the cold custard and place it in front of guests. Dip pretzels or other candies into the hot chocolate using long tongs. Or use any other kind of dipped treats you want. You can put anything in this dessert except fruit!