Azuki Matcha "Hidden Watermelons in the Ground" Chiffon Cake

Azuki-matcha-black sesame is my all-time favourite combination, and azuki is absolutely my family fave! It just so happened I was craving for some azuki on the morning I was supposed to try out a square chiffon hidden cake for my friend's daughter's birthday. On impulse, I scrapped my original idea to do strawberry yoghurt chiffon and changed it to azuki. The idea of azuki-matcha "watermelons" with black sesame seeds had me drooling! I decided to theme the cake as "hidden watermelons in the ground" with honey matcha chiffon cake and azuki flowers in the background. The watermelon skin will be a two-layered matcha-milk chiffon (to resemble the dark and light part of watermelon skin), and the watermelon flesh will be azuki chiffon with black sesame seeds (to resemble watermelon fruit and seed).

An important objective was to practise baking chiffon cake in large square tray (10-inches) without shrinkage. For this, I got some inkling from Nasi Lemak Lover's Pure Vanilla Sponge Cake to bake at a lower temperature at the start (she used 140°C for 25 min then 160°C for 30 min for an 8-inch pan) to have the cake rise slowly. From my previous experience with steam baking, I had also observed that steam baking chiffon at lowest rack at a lower temperature creates a nice smooth top with little shrinkage upon cooling. I used 150°C for 1h 10 min with steam baking for this chiffon with baking paper only at the bottom (to facilitate unmoulding of large square bottom) and let it cool right side up, following Kitchen Tigress' ogura blog post. I was quite happy this time I had no shrinkage of the chiffon upon cooling. The chiffon cake gripped well to the sides and maintained its height in the centre. There was little shrinkage at the sides that I needed to trim off :).

This hidden cake takes around 2 days to bake. Do keep an airtight container to keep the cake parts.

Ingredients

*You may choose to skip this section for "watermelons" if you only want to bake a chiffon in a large square tray with no tube without shrinkage.

For "watermelons"
4 egg yolks
27g sugar
51g vegetable oil
56ml azuki milk (28g azuki + 28g warm milk)
80g cake flour

5.3 egg whites (this is according to calculations for scaling, you can use 5 egg whites)
60g sugar
1/4 tsp cream of tartar

1. Preheat oven to 160°C. Prepare a tray of water at the bottom of the oven (I used the lowest rack to bake the cake).
2. Beat egg yolks with sugar with whisk till pale yellow before stirring in oil and azuki milk (azuki milk in left picture).

3. Next add in sieved flour and whisk till no trace of flour found.
4. Scoop over 8 tsp of batter and add 2 tsp matcha powder for green layer. Scoop over 8 tsp batter for plain layer. To the rest of the batter, add 1 tsp black sesame. You may opt to put a dip of red colouring for sweet pink colour or omit.
5. Meringue: Beat the egg whites with ¼ tsp cream of tartar till stiff peak, mixing in caster sugar in 2 additions.
6. Scoop over 16 tbsp meringue for green and plain egg yolk batter respectively. Fold gently into the respective batter. Fold the rest of the meringue into the azuki batter in 2 additions (the final matcha, plain, and azuki batter after folding in the right column).
7. Fill the bowls with a layer of green batter, followed by plain batter. Then fill the remaining space with azuki batter for the watermelons. Gently tap on table to remove air bubbles.
**8. Pour the remaining azuki batter into the 6-inch tray (lined at bottom and sides) for the flowers. **This is optional if you do not want to decorate the cake with flowers.
9. Steam bake the cakes in bowls for 15 min at 160°C then 15-20 min at 150°C. Bake the 6-inch tray cake for 18 min at 150°C (also lowest rack, steambaking). Note: I have a separate smaller oven for the 6-inch tray. Otherwise, you can also bake the tray at 160°C for 14+ min and remove.
10. As an experiment, I inverted 2 bowls and left the other 2 bowls upright. I was surprised there was no reduction in height with and without inverting! Unmould when they are cool.
11. Flip over the cake onto a clean baking sheet and unmould when cool.
12. Cut out the flowers and slice up the watermelons for baking into the big cake.

Chiffon in large 10-inch square tray

6 egg yolks

40.5g sugar

76.5g vegetable oil

84 ml warm milk

120g cake flour

1 tsp honey

2 tsp matcha powder

8 egg whites

90g sugar

1/4 tsp cream of tartar

1. Preheat oven to 150°C. Prepare a tray of water at the bottom of the oven (I used the lowest rack to bake the cake). Line bottom with baking paper (smooth and stick on with a little meringue).

2. Beat egg yolks with sugar with whisk till pale yellow before stirring in oil and warm honey matcha milk (1 tsp honey + 2 tsp matcha dissolved in warmed milk).

3. Next add in sieved flour and whisk till no trace of flour found.

4. Meringue: Beat the egg whites with ¼ tsp cream of tartar till stiff peak, mixing in caster sugar in 2 additions.

5. Fold the meringue into the cake batter gently in 3 additions.
*6. Arrange the azuki flowers at the bottom and gently cover with batter. Place the watermelon cakes in ring around the centre. Spoon the batter around their sides and over them. Run a chopstick around the sides of the tray to ensure there are no trapped bubbles.
*You may choose to omit this step if you just want to bake a chiffon in a large square tray with no tube.
7. Steambake for 1 hr 10 min.

8. Cool right side up for the first 20 min. Unmould and leave to cool (I followed Kitchen Tigress to cool right way up and there was no reduction in height!).
9. I sieved the top with matcha powder to recreate grass fields with flowers over the watermelons :).

Reviews for the cake was that it was very moist and soft! I personally thought the azuki-matcha-black sesame combination was "heaven"! :p It was finished in no time even though it was a huge 10-inch cake :).

This post is linked to the event, Little Thumbs up organised by Bake For Happy Kids, and My Little Favourite DIY, hosted by Tze of Awayofmind Bakery House at this post. 

With love,
Susanne