Preheat your oven to 175c

In a stand mixer fitted with your paddle attachment, beat your butter, oil and sugar until pale and fluffy 

Separate the eggs and add just the yolks, beat until just combined 

Mix  and sift the dry ingredients (flour, cocoa powder and baking soda)

Mix the food coloring with the buttermilk 

Alternate the dry ingredients with the buttermilk into the batter, starting and ending with the dry ingredients 

Add the vanilla to the egg whites until foamy 

Fold in the egg whites into the cake batter, pour in two separate 8” pans and bake for 30-40mins