This is the original red velvet cake recipe from the Waldorf Astoria. And its traditional icing which some people swear is the only frosting that should ever be used on a red velvet cake.
Beat the shortening (or butter), sugar, and eggs with the mixer until they are light and fluffy (2 to 3 minutes).
In a separate bowl, mix enough of the red food coloring with the cocoa powder to form a red-colored paste.
Add the food color/cocoa mixture to the shortening mixture and mix until combined.
In another bowl, whisk together the flour and salt.
Add ⅓ of the flour mixture to the shortening mixture and beat just until combined.
Then mix in ½ of the buttermilk.
Add the next ⅓ of the flour, followed by the other ½ of the buttermilk and then the last ⅓ of the flour, beating until combined between each addition.
Add vanilla, vinegar and baking soda to the shortening mixture in that order, mixing in between each addition.
Pour into 2 or 3 8-inch cake pans or 24 muffin tins.
Bake for 25 to 30 minutes for a 2-layer cake, or 20 to 25 minutes for cupcakes or a 3-layer cake. A toothpick inserted in the center of the cake should come out clean.
Let cool completely before icing.
Traditional icing
In a saucepan, stir together flour and milk making sure to get rid of any lumps.
Over medium heat, cook the flour and milk until very thick, stirring constantly.
Let cool completely.
In the meantime, beat the butter, vanilla and the confectioners' sugar together with the mixer until fluffy (2 to 3 minutes).
Add the flour mixture into the butter mixture together and beat until it is very fluffy. It should have a whipped cream texture when it is done.
Frost the cake
Spread frosting between the layers and over the top and sides of the cake. Or spread over the top of cupcakes with a knife.
Notes
For the best texture, make sure to use cake flour and sift it before measuring.
Using room temperature eggs and butter (or shortening) and then beating them with the sugar until they are light and fluffy will add air to the cake and prevent it from turning out too heavy and dense,
Bring the buttermilk to room temperature for the best results.
If you are using gel red food coloring instead of liquid, add it directly into the creamed shortening mixture. Then add the cocoa powder.
If you are using 2 racks in the oven, it is a good idea to swap the pans from the top to the bottom rack about half way through so they can bake more evenly.
For the icing, make sure that the flour and milk mixture is completely cool before adding it to the butter mixture. Otherwise, it will melt the butter which will ruin the icing.
This traditional red velvet cake icing is too soft to be piped, so it's not a good choice for decorating the cake