Grease two 8" round cake tins and coat with cocoa powder.
Sift plain flour, cocoa powder and baking soda in a bowl and mix.
Place butter and sugar in a second bowl mix until well combined, add eggs, one at a time, beating in between to combine. keep beating until it's smooth.
Add vegetable oil, vinegar, vanilla, buttermilk and red food colouring. Beat until combined and smooth.
Fold in the powdered dry ingredients from the first bowl with the batter made in the second bowl.
Divide batter between the two cake tins.
Bake for 25 - 30 minutes on the same shelf, or until a knife inserted into the centre comes out clean.
Make sure you rest for 10 minutes in the pan then turn out onto a cooling rack and allow to cool.
Finally spread buttercream icing between the two cakes until completely coated.