Makes about 8 cups
- 5 sticks (2 ½ cups, 565 grams) unsalted butter, softened
- 1 cup (75 grams) unsweetened cocoa powder
- ½ tsp kosher salt
- 6 ounces best quality unsweetened chocolate, melted and cooled
- 2 lb (about 7 cups) sifted confectioners’ sugar
- 1 Tbsp pure vanilla extract
- 1 to 3 Tbsp buttermilk or whole milk, as needed
- Storage: Store in an airtight container at room temperature for up to 2 days, in the refrigerator for up to 1 week, or in the freezer for up to 3 months. Return to room temperature and beat well before using.
Place the butter, cocoa powder, and salt in the bowl of a stand mixer fitted with the paddle attachment. Beat on low speed for 30 seconds until the cocoa powder has been incorporated into the butter and no dry patches remain, then increase the mixer speed to high and beat until glossy and smooth, about 1 minute.
Reduce the speed to low and slowly stream in the melted and cooled chocolate. Then, increase the mixer speed to high and beat until smooth.
Stop the mixer and scrape down the bowl with a rubber spatula. Add ½ cup confectioners’ sugar and mix on low speed until just combined, then increase the speed to high and beat for 30 seconds. Continue adding the sugar in this manner, stopping to scrape down the bowl occasionally. When all the sugar has been added, beat on medium-high speed for about 5 minutes to incorporate air into the frosting.
Reduce the mixer speed to medium, and add the vanilla. Add the buttermilk or milk, 1 Tbsp at a time, until the frosting is soft and smooth yet firm enough to hold its shape.