Preheat oven to 180ºC fanforced.

Cut the pastry sheets so they are a little bigger than the 20cm square baking tin. You can refreeze the unused pastry.

Place the pastry sheets on baking trays lined with non-stick baking paper. Place a sheet of baking paper on top of each pastry sheet and place another baking tray on each pastry sheet to act as a weight. Bake for 20–25 minutes or until golden. Cool completely on the trays. Using a serrated knife, trim the pastry sheets to 20cm square. (the same size as the inner size of a 20cm baking tin). 

Place the milk, cream, butter, vanilla and sugar in a medium saucepan with the wattle seeds over medium heat and cook until just boiling. Tiny bubbles will start forming a foam on top. Remove from the heat and allow to sit for five minutes for the flavour to infuse. Strain the liquid removing the wattle seeds. Combine the cornflour and water and whisk into the the egg yolks and then whisk this mixture into the warm milk mixture. Return to the heat, whisking, and bring to the boil. Cook, whisking, for 30 seconds–1 minute or until thickened. Remove from the heat and whisk for a further minute while the saucepan cools slightly. Place 1 pastry sheet (top side down) in the base of a lightly greased 20cm-square cake tin lined with non-stick baking paper. Make sure the baking paper goes across the bottom and up the sides for ease of removing the slice when cold. Top with the custard and the remaining pastry sheet (top side up) and press down gently. Refrigerate for 3–4 hours or until set. Dust with icing sugar and slice to serve.