In a microwave-safe bowl (or double boiler on the stove, stirring constantly) melt the chocolate on half power, in 30-second increments, stirring in between, until melted and smooth.
Remove from microwave and stir in the sifted cocoa powder until smooth. The mixture will be thick. Set aside.
In a medium saucepan over medium heat, combine the sugar, corn syrup, cream, salt and water. Stir constantly and bring to a simmer.
Simmer for 4 minutes. Remove from heat and stir in vanilla and butter.
Add the melted chocolate mixture and stir until smooth.
Serve warm, over ice cream.
Video
Notes
Chocolate: I use 10 oz (2 1/2 boxes) of semi-sweet Baker's chocolate or Trader Joes pound plus bars, but any high quality chocolate, like Ghirardelli chocolate chips, will work.Storing Instructions: Refrigerate in an airtight container for up to 3 weeks. Rewarm slowly in the microwave, stirring every 30 seconds, until pourable. Freezing Instructions: Cool completely then store in a freezer safe jar or container for up to 3 months. Thaw overnight in the refrigerator, then rewarm slowly in the microwave, stirring every 30 seconds, until pourable. Be careful not to let it get too hot or burn.