I’ve agonized a bit over this I must confess. There’s always pressure when you’re taking on a cultural icon…especially one you’ve never tasted. The filling of a vanilla slice bears an uncanny resemblance to pastry cream, only it’s often thickened to a rubbery degree. That’s in part due to the use of pre-packaged custard powder, of which we have none in the US of A, so we have to improvise. Here’s what I propose:
Procure an 8″ (8 inch) square cake layer pan with a removable bottom. 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.
Place the other pastry square on a rack over a sheet pan. Melt the poured fondant in a small saucepan. When it’s hot, add 2-3 tablespoons of simple syrup until it’s a pourable consistency. Pour it over the pastry and spread it promptly to cover any bare spots. Allow the layer to cool 5 minutes or so until the fondant sets up, then cut the pastry layer into portion-sizes squares or rectangles (depending on whether you’re an Aussie or a Kiwi). Hold them in anticipation of the final assembly.
Next, prepare the filling. In a small bowl combine the powdered gelatin with about 1 1/2 tablespoons of ice water and allow it to hydrate. Meanwhile prepare the pastry cream according to directions. EXCEPT in the final mixing step add the hydrated gelatin along with the hot milk to the egg foam. Finish the pastry cream and pour it into the cake layer pan on top of the bottom pastry layer. Promptly level it, then right away apply the fondant-covered pastry tops. Allow your creation to cool for an hour, then chill it in the fridge for at least two hours.
When ready to serve, put up the bottom of the cake pan, peel away the plastic wrap from the sides and, with a very long knife, slice the…thing…into pieces. Serve!