Kasutera cake is something I had before but I forgot how it taste like. Simply because usually you only get them as a gift from someone visited Japan.
In my version of this cake, I do not have macha powder (green tea powder), so I use 2 Japanese green tea bag and grind them into very fine powder, and sift them. It's kind of brown instead of green, because I don't use any color for the cake. and I find it taste better after the second day, because the cake will become more moist.

Ingredients :-
- 4 large eggs
- 2 yolks
- 4 1/2 tbsp fine brown sugar
- 3/4 cup bread flour (high grade flour)
- 1 tbsp green tea powder (I use 2 green tea bags, grind)
- 1 tbsp fine brown sugar
- 1/8 tsp salt
- 2 tbsp honey
- 2 tbsp milk
- 2 tbsp oil
- Sugar for sprinkling
Glaze :
- 1 tbsp honey
- 1 tbsp hot water
Method :-
- Preheat the oven to 170°C / 340°F, or 150°C / 300°F if you're using a convection oven.
- Cut the parchment paper so that it's large enough to fit the bottom and sides of the cake pan with a little excess. Fold it in until it completely covers the bottom and sides, leaving a it hanging over. (To make it stick to the pan, smear a little butter or shortening on the pan first.) Sprinkle a little sugar over the bottom, on top of the paper.
- Fill the pot with water and bring to a boil, then turn to small heat.
- Mix the milk and the 4tbsp of honey together, you may need to heat up the mixture for a few seconds in the microwave.
- Double sieve the flour, green tea powder, salt and 1 tbsp fine brown sugar.
- Whisk eggs, egg yolks and sugar in the warm bowl sitting over the pot of simmering water.
- Check the temperature of the mixture, you want to get the mixture between 30C. Keep whisking and checking the temperature. If it's becomes too hot, remove and whisk outside and return to the pot when it cools down.
- Keep beating about 8-10 mins until the mixtures becomes thick and shinny.
- Whisk in the milk and honey mixture. Add in flour with hand whisk a tablespoon at a time. Do it as quickly as possible, to prevent the foams collapse.
- Place oil in a medium bowl and spoon in a few spoonful of batter and fold together. When this is well blended, fold this mixture into the main batter.
- Pour the batter into the prepared pan.
- Baked for 40 minutes or until the skewer comes out clean.
- As soon as the cake is out of the oven, brush the top with the honey-water mixture.
- When the cake is cool enough to handle but still warm, lift out from the pan with paper and all, fold the paper to cover the cake. And put into plastic bag. Seal the bag and put into the refrigerator to cool the cake down.
- To serve, use very sharp knife to make clean cuts.
and http://www.justhungry.com/2006/08/oyatsu_and_kasutera_castella_a.html