Heat the chocolate in a water bath until it is liquid.
Then add the hazelnuts, rum, coffee and cocoa. Let cool slightly, but the mixture should still be viscous.
Beat the butter with the sugar until smooth and then mix together with the chocolate mixture.
Roll the rum balls of the desired size in the palms of your hands and roll them in the chocolate sprinkles, chopped pistachios or coconut flakes.
Then chill.