Preheat the oven to 160°C fan-assisted.

Grease and line a 9"x9" (22cm x 22cm) cake or brownie tin with baking paper. Make sure that the baking paper reaches up over the edges of the tin for easy removal of the brownie post-baking.

Melt the butter in a heat-proof bowl in the microwave.

Add in all the sugar and whisk to combine. Then pop the butter-sugar mixture back into the microwave for 30 seconds, whisk again and repeat 1-2 times. When you are done the sugar will have dissolved into the butter, and the mixture will have thickened. Allow to butter mixture to cool a bit.

Add the eggs, lemon juice and vanilla extract into the cooled butter mixture and whisk vigorously for at least 2 minutes with each addition. The butter-sugar-egg mixture will become lighter in colour.  Alternatively, you can beat the mixture using a hand-held electric beater for a minute. This step is crucial in obtaining the crackly blondie top.  

Add in the flour, cornflour, and lemon zest, mix until combined and spoon into the prepared tin. Knock the tin on the counter 3 to 4 times to knock out air bubbles.

Bake for 30 to 40 minutes, until the blondie has just set. This will be dependent on your oven.

Allow the blondie to cool in the tin for 30 minutes before lifting it out using the baking paper to cool completely on a wire rack.

Whisk together the icing sugar and lemon juice until you have a medium-thick pouring consistency to make the glaze. Drizzle over the cooled blondie. Slice into 16 to 25 pieces and enjoy!