1 1/3 c. (22 tbs.) salted butter, softened
2/3 c. shortening
6 oz. chocolate (melted and cooled to room temperature)
2 tsp. vanilla extract
2 lbs. (8 c.) powdered sugar
1/4-1/2 c. milk or cream
1-4 tbsp. corn syrup
Melt the chocolate on the stove in a bowl resting over a pot of simmering water; consistently stir the chocolate so it doesn’t burn. When the chocolate is completely melted set aside on the counter until it has completely cooled to room temperature.
First cream together the shortening and butter until smooth and there are no more streaks, then add the vanilla, and cream again until smooth and combined completely. Slowly add the chocolate and mix until there are no more streaks. Scrap down the bottom and the sides of bowl at this point to make sure there are no pockets of chocolate or butter. Gradually add the powdered sugar and blend thoroughly. At this point if your frosting isn’t the consistency you want just add the cream a tablespoon at a time or some corn syrup a tbs. at a time, blending thoroughly after each addition. Keep adding the cream or corn syrup until you achieve the consistency you desire.
This recipe tends to crust more quickly than regular buttercream, especially if cocoa powder is used. Keep a sharp eye on it and start testing after 5 minutes.
Instead of using melted chocolate you can also use cocoa powder or you can use a combination of both melted and powdered chocolate. This really depends on your preference of taste.
Never add any liquid to your frosting to thin it out until all the sugar in mixed in with butter and shortening mixture. If you do it before hand the frosting might turn out to thin, it is easier to thin frosting than it is to thicken it.