Into a saucepan, add the butter, heavy cream, and dark chocolate, and sift the cocoa powder and powdered sugar, and kosher salt.
Heat all the ingredients over medium heat mixing constantly until the mixture is smooth and melted.
Strain the mixture into a large bowl or baking pan to speed up the cooling process.
Cover the top with plastic wrap so that the plastic wrap is directly touching the top of the frosting. This will prevent skin from forming.
Let it cool at room temperature for 30 minutes, and then transfer it to the fridge to cool for another 1-2 hours. (depending on the thickness you are looking for)
Remove the frosting from the fridge and give it a mix with a spoon or a spatula. Use it for this matildas chocolate cake or for your dessert of choice!
Notes
Add ½ teaspoon of espresso powder to the mixture for a richer flavor and to enhance the delicious flavor of the chocolate.
If you feel like your frosting is too bitter, feel free to add 1-2 tablespoons of powdered sugar.
Use room-temperature ingredients like butter and heavy cream. This will make it easier for the mixture to melt together and get smooth and silky.