Chocolate Blueberry Cake (my son's birthday cake once again..)

My son's actual birthday falls on boxing day, so despite the disaster cake on Christmas Eve, i decided to bake him another cake (last min) so that our family can celebrate his birthday once again. I didn't plan on what design and the cake somehow ended up looking quite colorful - due to some designs which i piped and didn't like - then wanted to correct it and can't really do so and in the end the cake turned out in dual-tone green. Finally i ended up with this design...not exactly great..but i guess passable! Again, i decorated the cake with his favorite candy, M&Ms and Oreo's cookies!

Birthday Cake composed of chocolate sponge cake, whipped cream & blueberry filling. I wasn't sure if my son would eat the blueberry filling since he's one fussy boy. When he tried a bite, he liked it and ate up entire slice including the blueberry filling! :D Me Happy of course! Not easy to make him try new things!

I chose chocolate sponge cake last minute because I wanted something fast and at the same time, I wanted to try this recipe on youtube:-

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which was recommended by Gracekitchencorner . The chocolate sponge cake has a strong chocolate taste but i find the texture of the sponge cake not as soft as the usual sponge cake recipes that i have tried before but it is really quick to make. It is indeed rather spongy behaving every bit literally like a sponge! However imo, i feel that texture wise it is rather coarse.