Heat oven to 350°F.
Sift flour, baking soda, salt and cocoa together in bowl – set aside.
Cream sugar and shortening with a hand mixer on medium high speed until light and fluffy. This will take from 3-5 minutes.
Lower speed and add eggs, one at a time, beating only until smooth.
Stir in vanilla extract.
On medium speed, add milk and flour mixture alternately, starting and ending with flour mixture.
Scrape the sides of the bowl and beat 30 seconds more on medium.
Slowly add boiling water while beating on low speed, just until thoroughly mixed.
Pour batter into greased and floured 9x13 pan. (See Notes)
Bake 30-35 minutes or until toothpick inserted in cake comes out barely clean. If there's a crumb or two of cake on it, that's ok. It's ready. DO NOT OVERBAKE.
Set on cooling rack while you make the icing. (See Notes)