This is my take on the classic buche de Noel that uses my all-time favorite flavor in Asian desserts, black sesame. I grew up eating so many black sesame flavored desserts with my family. I just love the nuttiness and the striking dark color. Almond and orange zest complement black sesame beautifully, so they play supporting roles here.
For the almond orange sponge cake: Preheat the oven to 400 degrees F. Grease a 13-by-18-inch half-sheet pan with cooking spray and line with parchment paper. Grease the parchment paper and set aside.
Whisk together the flour, baking powder and salt in a medium bowl. Set aside.
Beat the egg whites in a stand mixer fitted with a whisk attachment on medium speed until foamy, about 1 minute. Slowly add 1/4 cup granulated sugar while beating. Continue beating until shiny medium stiff peaks form, about 2 minutes. Remove the egg whites to a medium bowl and set aside.
Add the egg yolks and remaining 3/4 cup granulated sugar to the same bowl of the stand mixer with the same whisk attachment (no need to wash). Add the almond and vanilla extracts as well as the orange zest. Beat on medium speed until pale yellow and doubled in volume, 1 to 2 minutes. Gently fold in the egg whites. Finally, fold in the flour mixture until just incorporated.
Spread the batter in the prepared pan. Bake until the top is springy, 10 to 12 minutes.
Use an offset spatula to loosen the edges of the cake. Immediately invert the cake onto a clean dish towel dusted with powdered sugar. Remove the parchment paper. Using the towel, fold the long end of the cake towards the center, continuing to roll the cake into the towel (this will help shape the cake when the buttercream is added). Transfer to a rack, seam-side down, to cool completely.
For the black sesame buttercream: Put the butter and confectioners' sugar in a stand mixer fitted with the whisk attachment. Beat on low speed until combined, then add the sesame paste, milk, vanilla and salt and increase the speed to medium. Beat until smooth.
For the decorations: Combine the coconut with the matcha powder in a medium bowl. Shape the marzipan into mushrooms.
Assembly: Unroll the cake on a clean work surface and remove the towel. Spread a third of the buttercream on the inner side of the cake, frosting all the way to the edges. Gently roll back into a log. Trim the ends of the roll, then cut a quarter of the log off on a diagonal. Place the larger log on a large serving platter. Attach the smaller log to the side of the cake with some buttercream to resemble a branch on the yule log. Spread the remaining buttercream on the buche de Noel to cover, but leave the cut sides unfrosted to show the swirl. Run an offset spatula or spoon over the buttercream for the appearance of rough tree bark. Sprinkle the matcha coconut around the cake to resemble moss. Place the marzipan mushrooms around the cake, gently pressing them into the frosting. Enjoy!