I posted this recipe a while back on my BBS site in Japanese. It's been a very very popular cake! The original recipe is a variation on a Gateau Yaourt.
For 2 mini loaf pans or 1 standard loaf pan:
Preheat oven to 375 F
1 1/2 cups all-purpose flour
3/4 teaspoon baking powder
a dash of salt (omit if using salted butter)
1 cup granulated sugar
1/2 cup plain FULL fat yogurt
1 teaspoon vanilla extract
1/2 cup of melted butter (do not use margarine)
1 to 2 Tablespoons powdered Matcha green tea
about a teaspoon of lukewarm water
1 Tablespoon cream (optional)
1) Sift together flour, baking powder and salt.
2) In a large bowl, combine eggs and sugar and mix with an egg beater until well incorporated. Add the sifted dry ingredients from (1) and continue mixing. Add vanilla and yogurt and mix well. Gradually add the melted butter and continue to blend until the cake batter is smooth.
3) In another bowl, add the powdered green tea and about a teaspoon of luke warm water. Mix this into a paste. If desired, add a tablespoon of cream and continue mixing this into a paste. Add about 1/4 to 1/3 of the cake batter from above. Blend until it is a solid green color. Taste a little bit of the batter for tea flavor. It should taste like really strong green tea. If not, correct it by adding more green tea (by making a paste as noted above.)
4) Prepare baking pans by lining it with parchment sheet(s) and/or coating it with non-stick spray.
5) Add the green tea batter to the plain batter with a rubber spatula. Make 1 or 2 large swirls with the rubber spatula, being careful not to over-do it. If you get too zealous, you won't get a marbled effect. You'll just get a green tea cake!
6) Pour the batter into the prepared pans, hopefully by alternating between plain and green batter.
7) Bake for 40 minutes at 375F.
The cake is best if you let it rest 1-2 days in the fridge. Wrap tightly with saran wrap and aluminum foil and let the flavors develop.
Use the finest quality Matcha that you can find as it affects the final flavor of the cake! Storage, handling, and freshness is important too as matcha is most fragrant when freshly ground. A reputable tea dealer I've purchased tea from had matcha stored in temperature controlled vaults similar to wine cellars!
Click on the bottom link for a pic of the cake.