This recipe has very similar ingredients to my usual chocolate fudge frosting, but the method is just a little different. In my usual recipe, you beat together the powdered sugar, vanilla, and milk, then add melted unsweetened chocolate and butter. At that point, the frosting is very dark and thin, and you need to beat it over a bowl of ice water to lighten and thicken the frosting. It can be temperamental: if the bowl gets too cold, the frosting becomes unspreadable, and then you have to adjust it with a little more milk.
The new recipe goes about it differently: you melt and slightly cool the chocolate, then beat it together with softened butter. (If you don't cool the chocolate a bit, it'll melt the butter.) Then you add the vanilla, a little cocoa powder (which amps up the chocolate flavors), and the powdered sugar. At this point, it's thick, dry, and crumbly, and you beat in about a third of a cup of buttermilk - a little more, if needed. For some reason, by inverting the process, you end up with a perfectly spreadable, lightened frosting that's thick enough to hold its shape when piped. And I like the hint of tang from the buttermilk. It's not quite enough to call attention to itself, but it's just enough to cut down on the sweetness of the chocolate. For what it's worth, the original recipe called for semi-sweet chocolate, but with five cups of powdered sugar, I didn't think the extra sugar in the chocolate was needed, so I used unsweetened.
I found the recipe online, paired with a cornmeal cake, and I think it sounds like a delicious combo! Meanwhile, it went perfectly with my chocolate cake, and I would make it again in a heartbeat.
Chocolate Buttermilk Frosting
(Makes about 4-5 cups)
4 ounces unsweetened chocolate, melted and cooled slightly
2 sticks butter, at room temperature
5 cups (20 ounces) powdered sugar
1/4 cup (3/4 ounce) cocoa powder
1 teaspoon vanilla
1/3 cup buttermilk
In a large bowl, cream together the melted chocolate and butter until smooth and creamy. Add the powdered sugar, cocoa powder, and vanilla, and begin mixing. Slowly add in the buttermilk until the frosting reaches your desired spreading consistency. If the frosting is too stiff, add a few more drops of buttermilk.