Preheat over to 325℉. Line standard size muffin tin with paper liners. Set aside.
Combine flours, sugar, matcha powder, baking powder and salt in the bowl of an electric mixer with a paddle attachment. Mix on low speed until combined.
Add butter cubes. Mix on low speed until mixture resembles crumbly, coarse sand. (This is the reverse creaming method.)
In a large measuring cup, whisk together egg, oil, and milk. With the mixer running on medium speed, add the wet ingredients to the dry in three additions. Scrape down sides of bowl before each addition. Mix until all ingredients are incorporated, being careful not to over-mix.
Divide batter among lined cupcake pan, filling a little over ⅔ full. Bake 20-25 minutes, until a toothpick inserted in the center comes out clean.
Transfer to wire rack to cool. Once cupcakes have cooled, stamp out center with a small round cutter. Fill cupcake cavity with sweetened red bean.