In the stand mixer bowl, combine salt, sugar, bread flour, green tea powder and instant yeast. Make a well in the center and add in the milk, egg, and tangzhong.

Fit the dough hook attachment on your stand mixer and begin mixing on medium speed until the dough comes together. Then add in the butter and continue to mix on medium speed. Keep kneading until the dough is smooth, not too sticky on the surface and elastic. I kneaded the dough for about 18-20 minutes. Each mixer may vary. When the dough is ready, you should be able to take a chunk of dough and stretch it to a very thin membrane before it breaks. When it does break, the break should form a circle.

Gather up the dough and put it in a bowl greased with oil. Cover with plastic wrap or a wet paper towel. Let it proof until double the size, about 40 minutes.

Deflate and divide the dough into 12 equal portions. Knead into ball shapes. Cover with cling wrap, let rest for 15 minutes.

Create balls with the red bean paste. Use however much you want for your filling. Make 12 balls.

Roll out each small dough ball with a rolling pin and flatten into a disc. Flip the dough so that the smooth side of the disk will be at the bottom (will be the outside of the bun.) Place a small red bean ball in the middle of the non-smooth side of the dough. Pinch the dough closed and knead into a ball shape with the seal facing down. Repeat this step of rolling and wrapping fillings with the rest of your dough. Place onto a baking tray, lined with parchment paper, covered with cling wrap. Let the dough sit for a second round of proofing, about 45 to 60 minutes, until double in size.

Bake in a pre-heated 320F oven for about 30 minutes, or until brown on top. Transfer onto a wire rack and let cool completely.