Preheat oven to 350° F. Grease two 9? round cake pans. Line with wax paper and grease and flour the pans.
Sift together flour, cocoa, baking soda, and salt in a medium bowl.
In a large mixing bowl fitted with a paddle, cream together the margarine and sugar until light yellow and fluffy. Beat in the eggs, one at a time. Beat in the vanilla.
Beat in the flour mixture, alternating with the milk, mix just until incorporated.
Pour batter evenly into the two prepared cake pans.
Bake in the oven for 40-45 minutes or until a skewer inserted in the center comes out clean. Allow to cool somewhat then remove from pans, remove wax paper and place on wire rack to cool completely.
Icing
Combine the first three ingredients in a medium saucepan and cook until a small amount poured into a cup of cold water makes long “threads”.
Meanwhile, beat 3 egg whites until stiff peaks form.
Keeping the mixer beating on a medium speed, add the hot syrup very slowly. Do not scrape down the sides of pan or bowl as this adds grainy crystals to the icing.
Beat until stiff peaks form again and then beat in 1 tsp vanilla.
Ice the cooled cake.
Recipe by Just a Smidgen at https://justasmidgen.com/2012/04/03/the-birthday-cake/