Mix oil and sugar along with vanilla essence together till light and fluffy. Add one eggs at a time beating till its mixed.
Add the rum to the buttermilk and let it stand for a a couple of minutes.
Sift together the flours, salt, baking powder, cocoa powder twice and keep aside.
Add the buttermilk and the dry ingredients to the sugar mixture alternatively and keep mixing well.
Pour the batter into a greased bundt pan (u can also use other pans see Lifefest's post for the timings of each pan)
Bake in a pre heated oven at 180C till a skewer comes out clean, mine took about 40 minutes or so.