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.
What is Hong Kong Napeolen Walnut Cake ?
Napoleon cake, also known as mille-feuille in French, is a classic French pastry and dessert. The name “mille-feuille” means “a thousand layers” in French, which reflects the numerous thin and flaky layers of puff pastry used in the cake. It is characterized by its delicate, crispy layers of puff pastry alternating with layers of pastry cream or custard. The top layer is often dusted with powdered sugar or glazed with sweet icing, which adds a touch of sweetness and elegance to the dessert. Now, the Hong Kong version is an adaptation of the French. Instead of using pastry cream, meringue, walnuts, and buttercream are used to make this thousand layers cake. It is a popular pastry you will see in Asian bakery stores. I went to several Chinese bakery stores in Chinatown in San Francisco, Seattle, and Toronto, and I saw this Hong Kong Napoleon walnut cake in every one of them!
Hong Kong Mille-Feuille Napoleon Walnut Cake
Ingredients
- 490 g puff pastry sheets I used Pepperidge Farm ready-to-bake sheets
Meringue:
- 60 g egg whites from 2 large size eggs, room temperature
- ½ tsp lemon juice or vinegar
- 70 g sugar
- ½ tsp vanilla extract
- 90 g roasted walnuts chopped
Buttercream:
- 70 g unsalted butter
- â…› tsp salt
- 30 g icing sugar more if you prefer sweeter
- ½ tsp vanilla extract
Instructions
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
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Nutrition
How to bake Hong Kong style Napoleon walnut cake
1. Bake meringue (one day before recommended). 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
2. 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
3. Add the toasted chopped walnuts and use a spatula to gently fold them in, taking care not to deflate the meringue too much
4. Divide the meringue into 3 portions and use an offset spatula to help you spread each portion to about 1/4-inch thick and about the size of the puff pastry sheets, which is about 9 x 4 inches (roughly_
8. 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.
6. Bake puff pastry: Preheat oven to 400 F (200 C) for conventional oven 380 F (190 C) for convection oven. I use ready-to-bake puff pastry sheets. 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. 
7. Place them on top of parchment paper-lined baking sheets. Poke the pastry with the tines of a fork all over to prevent air pockets from forming and uneven surfaces. Bake for 12-15 minutes or until golden brown. 
8. Remove from the oven and let the puff pastry cool down completely on a cooling rack before assembling
9. 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
10. Put 1st piece of puff pastry. Spread 1st portion of buttercream evenly on the puff pastry. 
11. Put one piece of meringue on top. Spread 2nd portion of buttercream on top of the meringue.
12. Put 2nd piece of puff pastry. Spread 3rd portion of buttercream on the pastry, followed by 2nd piece of meringue, 4th portion of buttercream. Then repeat this sequence until you end with spreading the last portion of buttercream on top
13. 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) 
14. 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
How to store Hong Kong Napoleon walnut cake
Traditional Napoleon cake is served the next day after the cake has time to “mature” in the fridge. The pastry cream will soften the puff pastry. For Hong Kong version of Napoleon walnut cake, it is best to serve it on the same day so you can enjoy the flaky pastry, crispy meringue, and smooth buttercream texture. If you do have leftover, keep them in an air-tight container for a day or two. The longer you keep them, the softer the puff pastry and meringue are going to be, which is still delicious honestly!
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