Cooking oil spray, to grease
2 sheets store-bought frozen ready-rolled puff pastry, partially thawed
100g white chocolate, melted
2 cups milk
1 cup thickened cream 75g unsalted butter
2 tsp vanilla extract with seeds
150g caster sugar
8 egg yolks
1⁄2 cup water
1 cup (300g) white fondant icing
75g good-quality dark chocolate, melted
Preheat oven to 180°C. Grease a 20cm square cake tin with cooking oil spray. Line base and sides with baking paper. Put each sheet of puff pastry between 2 pieces of non-stick baking paper, then sandwich between 2 flat oven trays. Bake for 25 minutes or until pastry is deep golden. Cool completely on a wire rack, then brush 1 side of each with melted white chocolate. Cut sheets to fit into prepared tin and put 1 sheet in base, chocolate-side up.
Put milk, cream, butter and vanilla in a medium saucepan and bring to a simmer over a medium heat. Meanwhile, put sugar, yolks and cornflour in a bowl and whisk until light and creamy. Stir in water. Pour in hot milk mixture, stirring well, then return mixture to saucepan over a medium heat and bring to the boil, whisking constantly until a thick custard forms.
Pour hot custard mixture over pastry and spread to flatten, then put second pastry square on top, chocolate side down. Allow to cool, then cover and refrigerate for at least 3 hours or overnight, or until firm.
Put fondant icing in a large heatproof bowl over a saucepan of barely-simmering water for 5 minutes or until warmed and spreadable. Working quickly, spread over top of slice using a warm palette knife. Put dark chocolate in a small zip-lock bag and snip corner tip. While fondant is still warm, drizzle chocolate in evenly spaced lines, then run a toothpick through lines in parallel direction to create a feather effect. Set aside for 10 minutes or until firm. Slice into 12 rectangles. Serve.