*I used my 10 cup capacity rice cooker which inner pot is 20cm in diameter

Line the base of rice cooker’s inner pot with baking paper. *Note: If your inner pot is in a good state, baking paper would be unnecessary.

Whisk Egg Whites in a large bowl until soft peaks form. Add Caster Sugar gradually, whisking for a few minutes until firm peaks form. Then add Egg Yolks and whisk until well combined.
*Note: You can beat Egg Whites, Yolks and Sugar all together until very thick.

Gradually sift Flour over the egg mixture while folding in with a large spoon, then add melted Butter and Vanilla, mix until just combined. Pour the mixture into the prepared rice cooker’s inner pot and press ‘Start’ button at ‘Cake’ setting.

Turn out on a wire rack. Carefully peel away baking paper, then leave to cool.

*Note: Top of the cake cannot be browned, but it looks fine upside-down. It took 40 minutes for my rice cooker to cook, but I could have taken it out a little bit earlier. This is absolutely the easiest & energy-efficient way to cook a sponge cake. You even don’t need a cake tin. Once you decorate it with cream or frosting, very few people would notice the cake is cooked in the rice cooker.