Flaky buttery puff pastry, sweet meringue, toasted walnuts and buttercream build these layers of decadent desserts. A Hong Kong version of the popular French Napoleon cake.
Prepare the meringue: (recommend to prepare the day before)
Get the eggs out of the fridge and separate them when they are still cold. They are easier to separate when they are cold. Let the whites come to a room temperature, this may take about 30 minutes or so. Save the yolks in the fridge for other use
Preheat the oven to 320 F (160 C) for conventional oven, 300 F (150 C) for convection oven. Line a baking pan with parchment paper
Beat the egg whites on medium speed until frothy, add lemon juice/vinegar and whip until it turns whitish and air bubbles are fine. Gradually add sugar as you beat, in 3 batches. I beat them at medium speed (speed 6 on Kitchen Aid). This will take a bit longer compared to beating at high speed. I used to do higher speed (speed 8), but the meringue is smoother and nicer when I maintain the speed of 6 and much more stable too. I highly recommend stopping several times to check on the consistency and scraping the sides of the bowl to make sure no sugar is left on the side of the bowl. Whip until you reach a stiff peak.
Add the toasted chopped walnuts and use a spatula to gently fold them in, taking care not to deflate the meringue too much
Divide the meringue into 3 portions and use an offset spatula to help you spread each portion to about 1/2-inch thick and about which is about 10 x 5 inches
Bake the meringue for 30 minutes and then reduce the temperature to 250 F (120 C) for conventional, 230 F (110 C) for convection oven and bake for another 1 hour. Turn off the oven, don't open the door and let them cool in there for at least 4 hours or overnight to crisp up.
Bake the puff pastry sheets:
Preheat oven to 400 F (200 C) for conventional oven 380 F (190 C) for convection oven
I use Pepperidge farm puff pastry sheets, which comes in two packs (about 490 grams/ 1.1 lbs) and you will need two. If the puff pastry sheets are frozen, thaw at room temperature until they are soft enough to be rolled out. Use a rolling pin to roll it out into a 12 x 18 inches rectangle. Cut into 3 equal pieces. Poke the pastry with the tines of a fork all over to prevent air pockets from forming and uneven surfaces.
Place them on top of parchment paper-lined baking sheets. Bake for 12-15 minutes or until golden brown.
Remove from the oven and let the puff pastry cool down completely on a cooling rack before assembling
Prepare buttercream:
Place the softened butter and icing sugar in a mixing bowl. Use a handmixer to whip the buttercream until pale and fluffy. Add vanilla extract and tiny pinch of salt and whip for another minute until combined. Roughly divide the buttercream into 6 equal portions for assembling later
Assembling:
Put 1st piece of puff pastry. Spread 1st portion of buttercream evenly on the puff pastry. Put one piece of meringue on top. Spread 2nd portion of buttercream on top of meringue.Put 2nd piece of puff pastry. Spread 3rd portion of buttercream on the pastry, followed by 2nd piece of meringue, 4th portion of buttercreamPut 3rd piece of puff pastry. Spread 5th portion of buttercream on the pastry, followed by 3rd piece of meringue (the last one), 6th portion of buttercream (the last one) on top
To serve:
Use a serrated knife to trim all 4 edges to make the assembled cake look neat. Cut into smaller serving pieces, about 7-8 pieces. Crumbled up the trimmings and spread on top of the cake as a topping (nothing is wasted)
Serve the cake on the same day if possible. Leftovers can be kept in an air-tight container for a day or two, but you will notice that the meringue and puff pastry will get softer the longer they sit after assembling. But I can tell you they are still very tasty with a softer texture, which some people like