In a large bowl, sift together the cake flour, sugar, baking powder, and salt.
Make a well in the center of the sifted ingredients and add the following, in this order: vegetable oil, egg yolks, water, and vanilla extract. Whisk together the ingredients in the well, then slowly start whisking in the dry ingredients, working from the center outward, until you have a smooth mixture.
In a large mixing bowl, beat the egg whites with the cream of tartar on medium speed until frothy, then increase speed to high and whip until stiff peaks form.
Pour the egg yolk mixture VERY gently and gradually, a small amount at a time, over the egg whites, folding until completely blended. (It is very important to be very patient during this part of the process so you do not totally deflate the egg whites, it can take up to 15 minutes or so to incorporate all of the egg yolk mixture.) Gently fold in the grated chocolate. Pour batter into an ungreasedtube pan and smooth the surface.
Bake for 55 minutes, then increase the oven temperature to 350 degrees F and bake for an additional 10 minutes.
Remove from the oven and cool the cake upside down until completely cool, then remove from the pan and transfer to a serving platter. The cake can be stored at room temperature, wrapped well in plastic wrap, for up to 5 days.
Notes
I needed approximately 7.5 large egg whites to make 1 cup.
Do not substitute regular cake pans or a Bundt pan for the tube pan - the cake will fall.