Gula Melaka Ogura Cake

This is a birthday cake for my sister. My family prefer light, airy sponge/chiffon cakes compared to butter/cream/fondant cakes, so I tried to make an Ogura cake. 

Original Recipe from BakingMom80, but I did some modifications as the original recipe was for a 6 inch square cake. A day earlier, I followed the recipe to a T, but used a 5x8inch rectangular tin instead of a 6inch square. Perhaps it was the larger eggs I used, but the batter overflowed the cake tin. On hindsight, I should have poured the excess batter to make cupcakes. 

Thus, for the actual birthday cake (I needed a 8 inch square cake to be enough for my family of ~20 pax), I used the following amounts: (text in red my own adjustments) 

(A)

5+1 egg yolk (I used large 60g eggs)

1 whole egg 

1/4 tsp salt 

60g canola oil 

70g+14g gula melaka - chopped into smaller pieces

20g+4g milk

75g+15g plain flour

(B)

5+1 egg whites

40g castor sugar 

1/4tsp cream of tartar

Steps

1. Grease and lined 8 inch baking tin. Prepare larger tin with boiling water (and a cloth to prevent baking tin from moving) for waterbath. Preheat oven to 150 degree Celsius.
2. Warm milk and add to the chopped gula melaka. Mix until dissolved. Strain to remove larger  particles.
3. In a large mixing bowl, whisk all ingredients in (A) except for plain flour, until light and fluffy. Set aside. 
4. In a separate, grease-free mixing bowl, beat egg whites until foamy. Add in cream of tartar, continue beating and add in sugar in 3 separate batches.  Beat until you attain firm peaks.
5. Fold the meringue into the yolk mixture in 3 batches. 
6. Pour batter into the cake tin slowly, letting large air pockets burst while pouring (this prevents the formation of large air pockets in the baked product). Smooth the surface of the batter with a spatula. 
7. Drop the prepared cake tin from a height of about 10cm from tabletop, to release any more air bubbles. 
8. Place the cake tin in the waterbath (I place a cloth between the waterbath tray and the cake tin to prevent any movement, which may happen if the waterbath level is too high)
9. Bake in the middle rack of oven at 150 degree Celsius for 70mins. 
10. Check doneness using a cake tester/satay stick. Once done, invert onto cooling rack for 5minutes, then unmould and remove baking paper before cooling upright. 

Cooling my 8 inch Gula Melaka Ogura cake