12ounces/340 grams good quality dark/bittersweet chocolate60-70% cocoa, chopped
8ounces/227 grams/1 cup unsalted butterroom temperature
1/4cupcocoa powdereither natural or dutch process are fine
1tbsppure vanilla extract
Melt the chocolate in the microwave on 50% power in 30 second increments, stirring each time - stop when it's about 70% melted, and stir vigorously to melt the rest. In my microwave, it took a total of 2 1/2 minutes. (Alternatively, melt in a heat-proof bowl set over a saucepan of simmering water - careful not to get a single drop of water in the bowl, or chocolate will seize). Allow chocolate to cool to room temperature.
Combine butter, cocoa powder, confectioners' sugar and salt in a stand mixer fitted with the paddle attachment. Beat on medium speed until well combined, about a minute. Reduce speed to low and incorporate vanilla extract, whipping cream and cooled chocolate, then turn speed back up to medium and beat for about 2 minutes, until pale and very fluffy. Pipe (I used Wilton Large Open Star tip) or spread onto fully cooled cake or cupcakes.
Frosting may be made up to 48 hours in advance - refrigerate until needed, then bring back to room temperature and beat again for a minute or two before using. Frosted cake may be stored at room temperature for up to two days - if it'll take you longer to eat, god bless your willpower and store the cake in the fridge.