How to change a chocolate cake recipe to a vanilla cake I have a recipe for a moist chocolate cake that requires 3 cups of all purpose flour and 1 1/2 cups of unsweetened cocoa powder.  I would like to turn this moist chocolate cake into a white cake and was wondering if I should substitute vanilla bean powder for the cocoa powder?  If that is possible, what amount would I use? Or can you suggest another substitute?  I've included the instructions 

Ingredients:
butter and flour for coating and dusting the cake pan
3 cups all-purpose flour
3 cups granulated sugar
1 1/2 cups unsweetened cocoa powder
1 tablespoon baking soda
1 1/2 teaspoons baking powder
1 1/2 teaspoons salt
4 large eggs
1 1/2 cups buttermilk
1 1/2 cups warm water
1/2 cup vegetable oil
2 teaspoons vanilla extract

instructions for cake:

*Preheat oven to 350 degrees. Butter three 9-inch cake rounds. Dust with flour and tap out the excess.
*Mix together flour, sugar, cocoa, baking soda, baking powder, and salt in a stand mixer using a low speed until combined.
*Add eggs, buttermilk, warm water, oil, and vanilla. Beat on a medium speed until smooth. This should take just a couple of minutes.
*Divide batter among the three pans. I found that it took just over 3 cups of the batter to divide it evenly.
*Bake for 30-35 minutes until a toothpick inserted into the center comes out clean.
*Cool on wire racks for 15 minutes and then turn out the cakes onto the racks and allow to cool completely.
*Frost with your favorite frosting and enjoy!
My honest answer is you don't without a lot of experimentation. 1.5 cups of cocoa powder is a significant portion of the recipe, taking it out will throw out every other measurement and there is no easy way to calculate what adjustments you'd need to make. Vanilla powder is much stronger a flavor than cocoa powder and cannot be a direct substitute. 

If you take out the cocoa powder you have to reduce the sugar level, but removing that much dry ingredient will make your cake too moist so you'd need to reduce wet ingredients to compensate. The buttermilk adds a sourness to it that counterbalances the bitterness of the chocolate, so that would need to be factored in. By the time you consider all that there are too many factors to make it worthwhile, you're better off finding a vanilla cake recipe. There are plenty out there which have buttermilk in them (I like buttermilk so I'd give that a try), I've had good luck with recipes using custard powder as well.