Preheat the oven to 180℃, line two 5 inch tins with baking paper and brush with oil, set aside.
In a small mixing bowl add the flour, cocoa powder, baking powder, baking soda, salt and mxi together until combined.
In a small glass add the milk and vinegar, stir and set aside.
In another bowl add the oil, mayonnaise, egg and whisk. Add the white, brown sugar, vanilla and whisk. Add the milk mixture and whisk.
Add half the dry ingredients and mix until partially combined, add the hot coffee and mix until smooth. Add the remaining dry ingredients and mix until combined.
Divide the batter between the tins and bake for 19-21 minutes until risen and tooth pic inserted into the center comes out clean.
While this is happening let us make the frosting by adding all the ingredients into a heavy bottom sauce pan and placing on low heat. Stir well making sure the chocolate is melted and the mixture is smooth, do not over cook and take it off the heat. let it cool completely (around 1 hour).
Once the cakes are done remove from the tin and let them cool completely before frosting. After the cake is cooled place one cake on a plate and top with the frosting that should now be thick and spreadable. Spread the frosting evenly over the cake and place the next cake on top. Frost the top of the cake and he sides in a rustic swirl like manner.
Slice and serve or just bite into it directly.