Prepare the pastry. Preheat your oven to 200C fan. Place the cut puff pastry on a sheet of baking paper on a baking tray. Dust ONE side liberally with icing sugar, then cover with another sheet of baking paper and another baking tray to weigh it down. Bake for 15-20 minutes. Then, remove the top tray, and if still not golden, dust with more icing sugar and bake for another 5 minutes until golden and caramelised (watch carefully so sugar doesn't burn). Turn down oven to 170c Fan.

Place the butter in a saucepan on a medium heat, stirring continuously for about 10 minutes, until browned and nutty. Immediately transfer to a large bowl. To the butter, add in caster sugar and vanilla bean paste and whisk to combine.

Once the mixture is cool, whisk in one egg at a time and the additional egg yolk until well combined.

In a separate bowl, whisk the flour, cinnamon and salt together, then fold this into the wet mixture until just combined.

Add the caramelised puff pastry to the bottom of a 23cm x 23cm tin lined with greaseproof paper, making sure the sugared side is facing up. Pour the blondie batter over this and smooth out, then bake for 15 minutes, until just starting to set.

For the custard: In a medium saucepan, whisk together the flour and milk until smooth. Add the sugar, cinnamon stick, water, lemon zest and vanilla. Cook over medium heat, stirring constantly, until thickened, about 5-7 minutes. Remove from heat and discard the cinnamon stick and lemon zest.

In a medium bowl, whisk the egg yolks. Slowly whisk in about ½ cup of the hot milk mixture to temper the yolks. Then whisk the tempered yolks back into the saucepan with the remaining milk mixture. Return to medium heat and cook, stirring constantly, until thickened enough to coat the back of a spoon, about 2-3 minutes more.

Pour the custard over the partially baked blondie base. Return to the oven and bake for 20-25 minutes, until the custard is set. Allow to cool completely before cutting into squares.