Preheat oven to 350°F Prepare 11 x 17 sheet cake pan with shortening and flour or baking spray. Combine the sifted flour and salt.
Set aside.
In a separate bowl combine the cocoa and food coloring, stirring until smooth.
Set aside.
Cream together the shortening and sugar, beating for 4-5 minutes at medium speed, until fluffy. Add the eggs, one at a time, beating for at least 30 seconds after each addition.
Add the cocoa/food coloring mixture.
Mixing until color is somewhat uniform.
Combine water, Saco Buttermilk Blend, vanilla, and Kahlua.
At low speed, alternately add the flour mixture and the buttermilk mixture to the sugar mixture.
Do not overbeat.
In a small bowl, mix the vinegar with the baking soda.
Stir briefly to mix.
Add to the cake batter.
Fold into the batter to blend well.
Do not beat.
Pour batter into prepared cake pan.
Bake for 20 minutes or until cake tester comes out clean.
Allow cake to cool before frosting.
Fluffy White Frosting
Cook the milk and flour in a heavy saucepan until very thick.
Cool, covered, in refrigerator until very cold.
Beat 2 sticks butter and 1 cup sugar for 8 minutes.
Add the chilled milk/flour paste and beat for another 4 minutes.
Add the vanilla in the last beating.
Frost Red Velvet Sheet cake when cooled.
Toast coconut on cookie sheet at 350°F for 5-7 minutes.