Combine flour, sugar and cinnamon in a large mixing bowl or mixer. In a small saucepan, combine shortening, butter, and water. Bring to a boil and pour over dry mixture. Mix until well incorporated. Add in buttermilk, then soda, then eggs, stirring well in between each ingredient. Gently fold in apples. Pour into a 15"x3" greased jelly roll pan. Bake at 400°F for about 20 minutes. Set on wire rack to cool.

Melt butter and add milk and vanilla. Add in enough powdered sugar to make a slightly thick frosting, but still thin enough to drizzle. Gently drizzle frosting over cooled cake.