1. Beat eggs, sugar, SP and vanilla with a mixer for about 10 minutes until fluffy.
2. Add the bananas, flour, baking powder, and powdered milk alternately to the egg mixture. Stir well.
3. Add in the cooled melted butter. Stir the bali with a spatula until well mixed and no butter settles to the bottom of the container.
4. Pour the dough that has been smeared with melted butter and lined with baking paper. Tap the dough a few times. Sprinkle the surface of the sponge with banana slices.
5. Bake the cookies in the preheated oven for about 45 minutes. Test the dough with a skewer, if it doesn’t stick then the cake is done.
After the sponge cake has cooled, it can be removed from the mold and then cut according to taste. Good luck and hope you like it!