2) Mix instant coffee with water set aside for later. Sift plain flour, cocoa powder, bicarbonate of soda and baking powder together, taking care that all the components are well combined and evenly distributed.
3) In the bowl of a stand mixer, mix the butter and shortening with paddle attachment on second speed until combined. Add caster sugar, sour cream, vanilla essence, coffee mixture and salt, starting on first speed and gradually moving to second speed until light and fluffy (approximately 8 minutes).
4) At one-and-a-half speed, add the whole eggs, in small amounts, until smooth and fully incorporated. Add dry ingredients and banana puree in staggering steps to the mixer and blend until well combined.
5) Pour into greased sheet pans or four (8-by26cm round) cake pans and bake for 30-45 minutes or until a toothpick inserted into the centre of the cake comes out clean.
This recipe was provided by professional chefs and has been scaled down from a bulk recipe provided by a restaurant. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore we cannot make any representation as to the results.