So alright, after a lot of fiddling I have a formula for the simple, day-to-day, down n’ dirty, semi-homemade, express version of the vanilla slice. It’s taken me three tries since there’s no American equivalent for Australian custard powder (who knew?). But this is should approximate the real deal as defined by several readers and a recent visiting Kiwi (note to non-experts, they call vanilla slices “custard squares” in New Zealand). Anyway, here’s what you need:
1 package store-bought puff pastry
2 boxes JELL-O vanilla pudding/pie filling (4.6-ounces each)
5 cups milk
1 ounce (1/4 cup) cornstarch (alternately two well-beaten whole eggs)
1/2 recipe simple icing made with passion fruit purée instead of water
Procure an 8″ (8 inch) square cake layer pan (one with a removable bottom is ideal). Line it with baking parchment. Preheat your oven to 400 degrees Fahrenheit. Roll out the puff pastry to a layer 1/8 inch thick or less, into a sheet measuring roughly 20″ x 10″. Cut it into two pieces roughly 10″ x 10″ (precision is not necessary at this point). Place the sheets on separate baking sheets and poke holes all over them with a fork to prevent much rising. Lay another sheet pan on top of each. Bake the dough sheets about 20 minutes. Remove the top pans and bake another 8-15 minutes until the pastry pieces are golden brown. When the pastry is cool, trim the pieces to 8″ square (the original pieces will have shrunk up some in the oven). Place one square in the bottom of the cake pan.
Next, prepare the filling. In a small bowl combine the cornstarch with about 1/4 cup of the cold milk. Or, for a smoother, more custard-like texture, beat two whole eggs well in a small bowl. Pour the milk into a medium saucepan. Whisk in the cornstarch mixture (or eggs) followed by the JELL-O mix. Whisk over medium-high heat until the filling mixture comes to a boil. Set the pudding mixture aside for 5-10 minutes to allow it to cool and thicken. Pour the filling into the layer pan. Allow the filling to sit in the pan a further 20 minutes to cool a bit more, then top with the second sheet of puff pastry. Cool the pan for an hour at room temperature, then place it in the refrigerator to chill, about another 2-3 hours.
When the pan is fully chilled, mix together the passion fruit purée and the powdered sugar. Spread the icing thinly on the top of the pastry sheet and let it set up a further 10-15 minutes. Slice and serve!