This buttercream is not as stable as others, meaning that getting it to come together can sometimes be tricky and it is more prone to melting and cracking once applied as frosting. Making sure all your ingredients are at room temperature is one trick to getting the buttercream to stabilize.
Confectioner's sugar gives this icing a smoother mouthfeel. You can substitute other solid fats in place of butter, but it will be less creamy and taste more bland.
A word to the wise: this buttercream includes uncooked egg yolks. If you're cooking for folks that might be sensitive to this (or if you yourself prefer not to eat raw eggs), skip this one, but hang around for later recipes on cooked buttercreams.
Classic Buttercream Frosting
Makes enough to frost a 9" cake or approximately 24 cupcakes
1 cup confectioner's sugar (or granulated sugar, or a combination of the two)
6 egg yolks, room temperature
1 cup unsalted butter, cut into 1 Tablespoon pieces, room temperature
1/4 teaspoon salt
1 Tablespoon flavorings, like vanilla, almond extract, or liqueurs
Beat the sugar and eggs on medium-high speed until they turn a lemon-yellow color and you get a very thick ribbon. Add the butter one tablespoon at a time, beating well between each addition. When all the butter has been incorporated, add the flavorings.
Buttercream is easier to work with when it's room temperature. If you're making it ahead of time, store it in the fridge and allow time for it to come up to room temperature before proceeding with frosting. If the buttercream is very stiff, even at room temperature, try beating in a few tablespoons of whole milk or heavy cream.
• For some excellent buttercream recipes and variations - not to mention a ton of delicious recipes to use them on - check out Sara Kate's cookbook, The Greyston Bakery Cookbook, available for $17.16 on Amazon!
Related: How to Frost a Layer Cake