Preheat the oven to 180 C, 350 F, Gas Mark 4. Prepare the bundt tin pan by gently coating with a layer of oil.
Mix Cake flour, cocoa powder, salt in a large mixing bowl.Sift them a couple of times and set them aside.
Separate egg white and yellow. Whizz the egg white for about 2 minutes until its get frothy and set aside.
Bring together Baking Soda & Vinegar and give it a good stir. The addition of Vinegar actives baking soda.
Using a handheld mixer with a paddle attachment, cream the melted butter & sugar for one minute. Now add oil, vanilla extract, egg yolk and whisk for a couple of times.
With the mixer on low speed, add the dry ingredients and buttermilk alternatively to the wet mixture until all of them are well incorporated. Now add Vinegar Baking soda concoction and mix well.
Finally, fold the egg white into the whole mixture. Stir to combine the mixture well.
Tip the whole mixture into the pan and place them on the middle shelf of the oven. Bake for 35-40 mins or until a skewer inserted into the centre comes out clean. Leave the cake to cool completely on a wire rack.
To prepare the Icing, Place the cream cheese along with butter into a mixing bowl.Whizz them with a paddle attached whisk in low speed until well combined.
Tip in Icing Sugar and beat for another one minute. Now add vanilla essence +double cream, mix well. Check for consistency.
If you are looking for a thicker consistency, add in more icing sugar. If you would like to make it slightly runny, carefully add in more cream, little by little as you combine.