Pre-heat the oven to 325°F.
In a large bowl, sift together both flours, cocoa, baking soda, baking powder, salt and sugar; set aside.
Grease and flour a 9-inch x 13-inch baking pan.
In the bowl of an electric mixer, beat together the vegetable oil, shortening and vanilla; beat well, at high speed with whisk attachment, until light and fluffy.
Add and beat the eggs, one at a time.
Fold in the dry ingredients alternately with the buttermilk.
It is very important to begin and end the additions with the dry ingredients.
Do not over mix the batter; as soon as it has no lumps in the batter, pour into the prepared baking pan.
Place in the pre-heated oven and bake for 30 to 35 minutes or until a wooden toothpick inserted in the center comes out clean.
Remove from the oven and allow the cake to cool in the pan.