- Melt the cooking chocolate in a glass bowl over simmering water.
- Remove the bowl and allow to cool slightly.
- Put both caster and brown sugar into the melted chocolate.
- Add in vanilla essence, egg and buttermilk. Mix well.
- Add in baking powder, flour and cocoa together.
- Put in the Kimball Mayonnaise and stir into the mixture until mixture becomes glossy.
- Once combined, pour the batter into a greased tray and bake in a preheated 180ºC oven for about 25-30 minutes.
- Cut into squares when cool.