1 cup heavy cream
6 Tbs. unsalted butter
3/4 cup sugar
2/3 cup brown sugar
pinch of salt
1 cup dark chocolate cocoa powder (make sure you use dark chocolate powder and not the regular -- I use Hershey's)
Combine cream and butter in a medium sauce pan. Stir over medium heat until the butter is melted and the mixture comes to a slow boil. Add the sugars, stirring until completely dissolved. Reduce heat and add salt and cocoa, whisking gently until smooth. Remove from heat and serve.
You can keep it in the fridge in an airtight container -- a spoonful in the middle of the afternoon is as good as a candy bar! Reheat over low heat or in the microwave at 50% power.