Heat the oven to 180°C (160°C fan).
Prepare a hemisphere tin by greasing and lining with greaseproof paper. I find it best to use 1-inch strips from one side of the tin to the other, gradually going around the tin until covered.
Whisk together the dry ingredients of flour, cocoa and salt and set to one side.
Add the butter, vegetable oil, vanilla and sugar to a bowl and beat until well blended (around 5 minutes).
Beat the eggs in one at a time.
Add the red food colouring.
Add the flour and dry ingredients alternatively with buttermilk, beating until combined. (Add dry ingredients in 4 stages and buttermilk in 3).
Add baking powder to a small dish, stir in vinegar and then beat in to cake batter for 10 seconds.
Pour batter in to prepared bowl and bake for around 1hr40 mins (reduce slightly for fan assisted) or until a skewer comes out clean.