Cream the butter on high in a large mixing bowl or stand mixer with the paddle attachment for about 90 seconds until creamy.
Add the vanilla extract and salt and mix on low speed until just combined.
Gradually add the powdered sugar, mixing on low until combined.
Add 2 tablespoons of heavy cream and mix until combined.
Add both cocoa powders and mix on low. Then, increase to medium and continue mixing until combined.
Add 2 more tablespoons of heavy cream and mix for 2 minutes or until you reach your desired consistency. Adjust with more cream to thin out the frosting if necessary.
This recipe will frost 24 cupcakes, a double 8-inch cake or 9x13 cake. For 12 cupcakes or a cheesecake, cut the recipe in half.
Notes
Storage
Store for up to 3 days at room temperature in an airtight container.
Refrigerate for up to a week in an airtight container.
Freeze for up to 3 months in an airtight container. Defrost in the refrigerator overnight.
Whip the frosting again before using it.
Tips
Your butter should be fully softened but not warm for the best frosting results.
Sifting your powdered sugar ensures even mixing and a smooth texture.
Adjust your frosting with very, VERY small amounts of heavy cream. You can always add more, but you can never remove it.