Method

• 1.
  Break the chocolate into a heatproof bowl and add the butter, then set the bowl over a saucepan of simmering water (don’t let base of bowl touch the water). Stir until the chocolate has melted and combined with the butter, then remove and leave to cool slightly.
• 2.
  Meanwhile, sift together the cornflour, cocoa, baking powder and a pinch of fine salt, then set aside.
• 3.
  Preheat oven to 180°C/160°C fan-forced, grease a 30cm × 20cm slice pan and line with baking paper.
• 4.
  In a stand mixer or large mixing bowl, whisk the sugar and eggs until thick and aerated - when the whisk is lifted out of the mixture, it should leave a ‘ribbon’ on the surface.
• 5.
  Stir the yoghurt and wattleseed into the cooled chocolate mixture. Add about a third of this chocolate mixture to the sugar and eggs and gently fold it in to loosen. Fold in the remaining chocolate mixture until just combined, trying not to knock out too much of the air.
• 6.
  Finally, fold the cornflour and cocoa mixture into the batter, adding a third at a time and being careful not to overmix. Pour the batter into the pan and sprinkle with dark choc chips.
• 7.
  Bake for about 25-35 minutes. Start to check it after 20 minutes, and at five-minutes intervals from then onwards - when you gently shake the pan, you want there to still be a slight jiggle in the centre.
• 8.
  Remove and allow to cool, then chill overnight before cutting into squares.