Preheat the oven to 160°C fan / 180°C / 350°F. Grease and line a 20cm (8") square baking tin with baking/parchment paper.
For the Brownie Batter
Melt the butter in a medium-sized heavy-based saucepan over medium heat, stirring until the butter melts. Add the sugar and cocoa powder and mix well until combined. Take off the heat and pour the mixture into a large mixing bowl.
Add the eggs to the bowl and whisk well to combine. Add the flour and fold until just combined. Pour the mixture into the base of the prepared baking tin.
For the Blondie Batter
Melt the butter in a medium-sized heavy-based saucepan over medium heat, stirring until the butter melts. Add the white and brown sugars and stir well until combined. Take off the heat and pour the mixture into a large mixing bowl.
Add the egg and vanilla extract to the bowl and whisk well until combined. Add the flour, baking powder and pinch of salt and fold until combined.
Drop spoonfuls of the mixture over the brownie batter in the tin and swirl 4-5 times with a skewer or knife.
Bake in the oven for 35-45 minutes. Leave the tin to cool for 20 minutes, then cool completely before cutting it into 16 squares.
Recipe Notes
Storage
Keep the Brownie Blondies stored in an airtight container for 3 days.