¼ t cream of tartar (This is a stabilizer that helps keep the frosting smooth).
4 egg yolks
6 oz semisweet chocolate (1-ounce squares are the simplest and most accurate option)
¼ cup strong coffee (You may also use 2 oz espresso or 1 t of coffee or mocha extract)
¾ lb butter
Chocolate candies, shavings or sprinkles for decoration (optional)
Instructions
Combine the sugar, water and cream of tartar in a saucepan, and boil until syrup reaches 240F on a candy thermometer. If you use a candy thermometer, you'll know this stage as "soft ball" which is between 234F-240F.
Beat the egg yolks until they are light and fluffy. Add in the sugar syrup a little at a time, continuing to stir until the mixture is stiff.
Melt chocolate and coffee together in a bowl set over hot water, stirring occasionally. Allow to cool slightly.
Beat the egg yolk mixture into the chocolate a little at a time until there's a uniform consistency. Chill the frosting in the refrigerator until it reaches the proper texture.
After frosting your cake, garnish with chocolate shavings, sprinkles or m&ms for a festive look and a little extra crunch. (optional).
Tip: If the frosting becomes too stiff in the refrigerator, stir in a small amount of milk to thin the mixture.
Recipe by Finesse Corner at https://finessecorner.com/rich-mocha-buttercream-frosting/