I fall in love with this cake since first time I had it at MUJI café

If there were just one recipe that you can make for this holiday season, what it could be?

“Purple Sweet Potato & Chestnut Roll” A cotton soft vanilla sponge cake, loaded with Chestnuts Cream and earthy Purple Sweet Potatoes.
I thought this cake will brings both hearty comfort and seasonal decadence to holiday table.

I’m not a fan of Chestnuts but this cake turned me into a Chestnuts Lover. The Purple Sweet Potatoes paste not only inviting but also tasty 🙄.

And since Christmas is coming soon, I developed the cotton sponge cake with Spinach Powder that I really love.

The earthy flavour of the spinach bring freshness and goes very well with the sweetness from the sweet potatoes. And yes, the vibrant purple and green colour is more lovely too 😘.

If you really can’t find Spinach Powder, you can substitute it with Matcha Powder, It really doesn’t taste so much different.

I found spinach brings more vibrant colour while Matcha has a slightly bitter taste.

And for the Chestnut Cream filling, don’t bother using unpeeled Chestnuts, nowadays roasted Chestnuts without shell is available anywhere and it’s tasty too.

I use stabilized whipped cream in this recipe. This method produces the perfect whipped cream that you love, but with a stabilizing agent, which means that it won’t fall flat or melt if it sits around for a while.

The little secret is a bit of unflavoured Gelatine. This won’t change the flavour or texture either, it simply provides some staying power.  

It’s a beautiful dessert with dazzling colours; the bright green colour of this spinach cake match perfectly with Christmas time, since it’s so Grinch-like 😂

The cake so soft-moist and not too sweet, with the creamy earthy Chestnut filling…
It really has a nice purple colour and very nutritious too ☺️

I hope this cake can give you an inspiration for your upcoming Christmas, I hope you learn something
Please give it a try and share with me what do you think about it?

Love you All!!

PURPLE SWEET POTATO & CHESTNUT ROLL
Yield: One (23 x 23) cm Square Pan
Active time: 1½ hours
Total Time: 2½ hours

INGREDIENTS
Purple Sweet Potato Paste:

• 250 g Purple Sweet Potatoes
• 100 g Heavy Cream
  

Spinach Sponge Cake:

• 55 g Egg Yolks
• 15 g Caster Sugar
• 45 g Milk (warm)
• 30 g Vegetable Oil
• 1/2 tsp Vanilla Extract
• 1/2 tbsp Spinach Powder
• 2 tsp Hot Water
• 45 g All-Purpose Flour
• 10 g Corn Starch
• 90 g Egg Whites
• 1/4 tsp Cream of Tartar
• 45 g Caster Sugar
  

Chestnut Cream:

• 1/2 tsp Unflavoured Gelatine Powder
• 3/4 tbsp Cold Water
• 175 g Heavy Cream (cold)
• 30 g Icing Sugar
• 1/2 tsp Vanilla Extract
• 50 g Roasted Chestnut (chopped)
  
  

INSTRUCTIONS
Purple Sweet Potato Paste

1. Under running water; scrub the sweet potatoes to remove any dirt and then steam them for about 30 minutes or until very soft. 250 g Purple Sweet Potatoes
2. Take it off from the heat, let it cool completely before adding the Whipped Cream.
3. Peeled off the cooked sweet potatoes and mash it until smooth.
4. Add in the whipped cream and mix until well combined. 100 g Heavy Cream
5. Using strainer, sift the paste mixture (this step is important, you don’t want lumps or any hard fibre in your paste). Pass mixture through a sieve.
6. Place the sifted paste into a pipping bag, cut off the end; then drop it into another bag that is fitted with this basket weave nozzle. Store the paste in the fridge while preparing the cake.

Spinach Sponge Cake

Before you start, make sure that the bowl and beater grease-free; because any residue of fat will prevent egg whites from beating up properly (wipe the bowl and beater with Vinegar or Lemon Juice to remove the left over grease).

1. Preheat the oven to 150°C.
2. Line the pan with a Parchment Paper (bottom and sides).
3. Combine the egg yolks and sugar, mix until the sugar dissolved. 55 g Egg Yolks; 15 g Caster Sugar
4. Pour in the warm milk along with vegetable oil and vanilla extract; mix again until well combined. 45 g Milk (warm); 30 g Vegetable Oil; 1/2 tsp Vanilla Extract
5. Dilute the powder with some hot water (if you really can’t find Spinach Powder, you can substitute it with Matcha Powder). 1/2 tbsp Spinach Powder; 2 tsp Hot Water
   Add in to the egg yolks mixture, mix it really well.
6. Sift in the All-Purpose Flour along with Corn Starch in two batches; set aside. 45 g All-Purpose Flour; 10 g Corn Starch
7. For the egg whites
   In another bowl; whip egg whites for a few second. 90 g Egg Whites
   Add in Cream of Tartar and mix again. 1/4 tsp Cream of Tartar
   When the egg whites started to get foamy, slowly add in the sugar in 3 batches and continue mixing until it reach a firm peaks (peak fold like a bird’s beak). 45 g Caster Sugar
8. Add the egg whites mixture to the yolks batter in 3 batches.
   Add the first batch, mix it really well to loosen the batter
   Continue with the second and third batches; using spatula fold gently, make sure there’s no egg yolks batter left at the bottom of the bowl (do not over mixed or the batter will deflated).
9. Pour the batter into prepared pan. (23 x 23) cm Square Pan
   Shake a bit and tap the pan a few times to remove air bubbles
10. Bake in the preheated 150°C oven for about 25-30 minutes.
11. Once it’s done, tap the pan a few times so the cake doesn’t shrink too much
    Place a piece of parchment paper with a cooling rack on top; turn it over
    Take it out from the pan, peel the parchment paper on top, place a new parchment paper on top to prevent the cake from dying out; and let the cake chilling out until it cools completely.

Chestnut Cream

1. Chopped Chestnuts into fine pieces (feel free to use food processor), set aside. 50 g Roasted Chestnut
   Don’t be tempted to cut it big, it won’t taste good, you will find an unpleasant gritty texture on your cake.
2. Mix Gelatine with some cold water. Let the mixture sit for about 5 minutes to “bloom” (it will be thick and semi-solid).1/2 tsp Unflavoured Gelatine Powder; 3/4 tbsp Cold Water
3. While the gelatine blooming, you can start beating the heavy cream.
   You can put your bowl in the freezer before mixing or just place a bowl of ice water under your mixing bowl (especially if the weather in your place is quite hot).
   Mix the heavy cream and icing sugar, beat for about a minute; set aside. 175 g Heavy Cream (cold); 30 g Icing Sugar
4. Heat the bloomed gelatine in the microwave or on the stove until just melted (it only takes about 5-10 seconds).
   Slowly add the gelatine into the cream mixture, as the mixer is running.
   Add in Vanilla Extract and Continue beating until you reach medium-stiff peaks. 1/2 tsp Vanilla Extract
   * As it sits over ice water or in the fridge, it will set up a little more, and it will last significantly longer than regular whipped cream.
5. Mix the chopped chestnuts into the Whipped Cream, fold until well combined.

Assemble and Decorate

1. Use the bottom part of the cake for the outside.
   Spread 2/3 of the chestnuts cream over the cake; roll it up; use a ruler to pull it tight (kindly follow video instructions)
   Wrap the cake and then store in the fridge for at least 1 hour to set.
   * Store the rest chestnut cream in the fridge
2. After 1 hour, take the cake from the fridge
   Trim both ends to make it prettier
   Spread the remaining Chestnut Cream on the surface of the cake
   Pipe the purple sweet potato paste on top (horizontally), decorate as desire.
   
   

NOTES

1. If you really can’t find Spinach Powder, you can substitute it with Matcha Powder. I found spinach brings more vibrant colour while Matcha has a slightly bitter taste.
2. The cake should be stored in the fridge (in an airtight container). Best served on the day it’s made; it can be store in the fridge for 3-4 days.