For the matcha green tea génoise:
Preheat the oven to 375°F.
Separate the egg yolks from the whites.
In a mixing bowl, beat the egg yolks with 1 cup powdered sugar until you get a pale yellow foam; the texture of the egg yolk will be thicker. Add the almond extract.
In a separate bowl, combine the flour, potato flour and baking powder. Sift the dry ingredients.
Combine the egg yolk mixture, dry ingredients, 6 tablespoons butter and matcha tea powder.
In another bowl, add salt to the egg whites and whisk for about 2 minutes at low speed. Add ½ cup powdered sugar, increase the speed of your mixer and keep beating for another 2-3 minutes until it forms soft peaks. Don't over-beat or the texture will become grainy.
Using a silicone spatula, mix 1/3 of the whipped egg whites into the egg yolk mixture to soften it. Add the rest of the whipped egg whites and gently fold them in to get an airy batter.
Apply a thin layer of oil to a non-stick jelly roll pan, previously lined with parchment paper. Pour the génoise batter; even it out using a spreader. Bake for 5 minutes at 375°F; lower the temperature to 350°F and bake for another 5-7 minutes. The texture of the génoise should be very soft.
Allow to cool for about 15 minutes. Cover the génoise with another piece of parchment (make sure it's much larger than the size of the jelly roll pan), place another baking sheet or flat board on top and invert the cake. Remove the still-warm baking sheet, gently remove and discard the old parchment paper and replace it with a large kitchen towel. Roll the cake with the towel and form a log. Let the cake cool completely (while preparing the butter-cream ).
For the vanilla butter-cream:
In a bowl, sift the remaining powdered sugar.
In a medium-sized bowl, using a hand-held mixer, whip cream cheese with vanilla soymilk to soften it. Add 6 tablespoons butter, condensed milk and the powdered sugar until the texture is even. Add vanilla extract and beat for another 2 minutes until the texture is smooth and creamy.
For the roulade (génoise + butter-cream):
Once cooled, unroll the cake and remove the kitchen towel. Using a spreader, spread a thin layer of butter-cream onto the génoise cake, stopping 2 inches before the end of the rectangle (the butter-cream will spread eventually out to the ends). Start rolling the cake, by lifting the parchment paper underneath the cake (as a guide). Form a log. Wrap the log with the parchment paper and chill in the refrigerator for at least 2-3 hours.
Un-wrap the parchment paper from the cake roll, leaving 2 rectangles of paper beneath the cake (for easy release later). Trim about 1 inch on each side of the cake roll and discard the trimmings (we ate them!).
Cover the cake roll with a thick layer of butter-cream and smooth it out using a spreader. Using a cake decorator, score long lines along the length of the log, imitating the texture of wood. Decorate with vanilla chips. Pipe or spoon a little mound of butter-cream on top of each chip and sprinkle the top with green-colored sugar to repeat the green-themed color in the génoise cake. Remove and discard the 2 liner pieces beneath the cake.
This step is optional. To cover the "mess" at the bottom of the cake, I concealed the butter-cream flaws with chunks of candied nuts under the cake. Chill in the refrigerator for another hour.
Serve with a cup of green tea.
Depending on the measurement of your baking sheet, make sure not to over-fill the cake with butter-cream. When spreading the butter-cream, make sure not to spread too much at the edges of the cake so it doesn't burst on the side when rolled. I made a mistake and didn't fill enough though, so I ended up with leftover butter-cream.
When you start to roll the cake, it's essential to roll it tightly so you don't have any air gaps when serving the roulade.
Matcha is Japanese green tea powder. I buy mine at Teavana in the Stanford Shopping Center, in Palo Alto, California. You can also find it online. As soon as your matcha tea box is unsealed, store it in the refrigerator or in the freezer because of its short shelf life. To check for quality, matcha should have a beautiful green color. If it's yellow and dull, it's time to toss it. You can use it often in baking for macarons, cakes, cookies or custards or you can turn many pastries into a nice green color. Be creative on St. Patrick's day and Halloween!
Similar to other cake recipes, I use potato flour for a lighter, fluffier result.
Sifting dry ingredients helps to get rid of lumps of flour and also to aerate the mixture when liquid is added. It's very important for all of your baking so you get a moist result.
I decorated the cake by creating long stripes using a cake decorator I recently bought at Daiso, the Japanese version of a 99-cent store. If you don't have one, you could simply use a spreader or a fork to score lines along the length of the log.
To ensure that the log doesn't crack, roll the génoise in a kitchen towel while it's still warm.
This cake is also a tradition for Christmas, called Bûche de Noël.