Gale Gand Chocolate Blackout Cake

Cake:
Preheat oven to 375
Butter two 9 in round cake pans and coat lightly with flour
Line bottom with parchment
In a standing mixer fitted with the whisk, beat the 1 stick of butter with the shortening until creamy. Add the sugar and beat at medium speed until fluffily about 3 minutes. Add the eggs, one at a time, beating well between additions. Add the vanilla. At very low speed, beat in the cocoa powder, baking soda, baking powder and salt. Add the 2 1/4 cups of cake flour and the milk in 3 separate additions. Divide the cake batter between pans and bake in center of oven for 30 min. Let cakes cool.
Filling:
In a large sauce pan, combine 2 1/2cups of the water with the sugar, corn syrup and cocoa powder and bring to boil, whisking constantly. In a bowl, whisk the cornstarch with the remaining 1/2 cup of water until smooth, whisk into the cocoa mixture. Cook over moderate heat, whisking until very thick, 3 min. Off the heat, whisk in the butter, vanilla and salt. Place a sheet of plastic onto the surface and let cool, and refrigerate, 45 min.
Half each cake layer. Break up less attractive top cake layer and transfer to a food processor, and pulse to crumbs. Set one cake bottom on cake plate and spread with 1 1/2 cups filling. Add another layer and repeat. Add final layer and cover entire cake with remaining filling. Pat the crumbs all over the cake. Refrigerate 1 hour.