The Polish recipe calls for budyn, a powdered custard which might be tricky to find outside of Poland, so I used thick pouring custard instead. You can bake the pastry form-free or if you happen to have a 30cm x 20cm cake tin, use that. You can work with the dough ball while still warm, for flaky pastry, allow the dough ball to cool completely to room temperature before adding eggs. This will help create the layers.
For the choux pastry:
125gunsalted butterextra for greasing
For the vanilla custard cream:
750mlthick pouring vanilla custard
unrefined icing sugar
To make the choux pastry:
In a medium saucepan bring water and butter to a boil.
Add flour and mix vigorously with a wooden spoon until the mixture comes away from the sides and forms a ball. This should only take a few seconds.
You can work with the dough ball while still warm, for flaky pastry, allow the dough ball to cool completely to room temperature before adding eggs. This will help create the layers.
Transfer dough to a mixing bowl, add eggs one at a time and beat with an electric mixer until glossy and smooth.
To bake the choux pastry:
Preheat oven to 200C. Grease a large sheet of non-stick baking paper with extra butter.
Spread pastry into a rough rectangle until the dough is only a couple of centimeters thick. Dip a spoon or spatula in some warm water to stop it from sticking to the dough when spreading.
Place in the oven and bake for 25 minutes.
When ready, remove from the oven and allow to cool on the tray placed on a wire rack.
In the meantime, make the vanilla custard cream:
Place cream into a mixing bowl and whip with an electric mixer until it's fairly stiff - be careful not to overwork as it will turn into butter.
In a large saucepan, combine custard, eggs, flours and vanilla extract. Whisk until smooth.
Place over low heat and cook, whisking, until the custard thoickens.
Cool to room tempereature, whisking from time to time to prevent the skin from forming.
Add whipped cream to the mixture and whisk through.
To layer vanilla custard slice:
Using a sharp bread knife, cut the pastry in half, the two sides will be yor top and bottom.
Spread custard cream over one layer, leaving a 2cm edge around and top with another pressing down gently.
Trim edges if you want to get perfect squares. Otherwise skip this step if you prefer a more rustic look.
Using a sharp bread knife, cut the slice into 8 even squares. Dust with a little icing sugar and serve.
Tip: store the slice in the fridge and consume within 2 days. Bring to room temperature before serving. You may need to re-dust with some icing sugar.