In a large bowl with an electric mixer, cream the shortening and room butter together. Add cocoa and vanilla extract. Gradually add confectioners’ sugar, one cup at a time, beating well on medium speed. Scrape sides and bottom of bowl often. NOTE: When all the confectioners’ sugar is mixed in, icing will appear dry. Add milk and continue beating at medium speed until light and fluffy.
Keep buttercream icing covered with a damp cloth or in a sealed container until ready to use. Do not refrigerate it if you are going to be icing your cake within a few hours. Do refrigerate the icing if you are making the icing for future use. You will need to bring the icing back to room temperature before icing your cake.
Refrigerate your icing in an airtight container. It can be stored for up to 2 weeks. Please rewhip on low before using or Spoon Smash it in a large bowl. Move a large spoon back and forth or side to side to smash the sponge. Do this until all the icing is an equal, smooth consistency. Icing often gets a spongy look to it and the “bubbles” need to be diminished. You will be glad you did when you get compliments on the look of your decorated cake!
Dark Chocolate Icing: Add 3 or 4 more unsweetened chocolate squares (up to a total of 7, or a scant cup sifted cocoa powder). You will probably need to add a tablespoon of milk to thin out the Chocolate Buttercream for ease of spreading. Use your own judgment for this. I personally like a softer icing for spreading and piping.
YIELD: 3 cups - Makes 1 small batch enough for covering an 8-inch cake.
* I prefer to use chocolate squares over the cocoa powder. The texture is smoother to me.
** Add 3 to 4 tablespoons of a light corn syrup per recipe to thin for icing cake. Start with 3 tablespoons and see if you like working with it.
Chocolate Buttercream Icing Recipe: https://whatscookingamerica.net/PegW/ButtercreamRecipes.htm