How to make the world's softest butter sponge cake (Castella Cake 古早味蛋糕)

️This is a great butter sponge cake to make as it really tasty, very soft and fluffy cake️, a sight to behold, with chocolate and butter sponge swirls creating a fun, simple and beautiful cake that delivers on flavour as well as appearance, the flavour and texture of this sponge is truly amazing and everyone will enjoy it.

Ingredients
Makes 1 (PME round cake pan 6-inch)

(A)
• 35g salted