J making fluffy sponge cake for birthday

In the past I always make pound cake as our birthday cake because it’s does not require much techniques and gives a good outcome. This time I would like to try an advanced level (well, it’s advanced for us) by making a fluffy sponge cake. We followed The Home’s Cook Kitchen Fluffy Sponge Cake .

Turned out it did not feel like fluffy at all. Oh well. We’ll try and see what can be improved next time.