Preheat your oven to 180 degrees, fan bake and line 2 baking sheets with baking paper.

Place the sheets of pastry onto the prepared baking trays, Then use a fork to make small indentations all over the surface.

Bake for 15 minutes turning half way through. The pastry will be lightly golden on the surface cooked through.

Remove the pastry from the oven and, While it is still warm, press flat it flat. You can use a sheet of baking paper and a clean tea towel or another baking sheet to do this.

Line a square cake pan (the size of your pastry or slightly smaller) with baking paper. Make sure that there is enough excess paper to lift the slice out later.

Use a large knife to trim the pastry to just fit inside of your lined cake pan. Set aside while you prepare your custard.

Combine the custard powder and sugar in a large saucepan add 1/2 cup of the milk and mix well. Make sure that there are no lumps of custard powder remaining.

Add in the remaining milk and mix well .

Heat the mixture on a medium heat, stirring constantly until the mixture is fully thickened. Your custard should be a similar constancy to a thick yogurt. This should take about 5-10 minutes.

Place one of the pastry pieces in your lined cake pan before pouring over the hot custard.

Spread the custard out evenly and then place the other pastry layer on the top.

Place your custard slice in the fridge to cool.

To make the icing, combine the icing sugar, vanilla and a little bit of milk into a small bowl and mix well. The icing should be smooth and spreadable. Add more milk of icing sugar if necessary

Spread the icing evenly over the top layer of pastry and return to the fridge to set fully.

When the slice is fully set (at least 3 hours after pouring) you can remove it from the cake tin. Use the excess baking paper to carefully lift it from the pan. Use a serrated knife to slice the custard squares into 12 even pieces.