Combine the yeast, sugar and warm milk in a bowl. Give it a stir and leave for a few minutes until the yeast becomes bubbly.
Add the flour, salt, egg and oil into a stand mixer bowl fitted with a dough hook attachment.
Pour in the activated yeast mixture, lightly cooled tangzhong mixture, and knead until the dough becomes smooth, shiny and elastic.
The dough will be slightly tacky and you may want to finish kneading the dough with your hands.
Transfer the dough to a lightly greased bowl and cover with a cloth or plastic wrap.
Let the dough rise in a warm location, anywhere from 1-1.5 hours, or until doubled in size, depending on how warm your kitchen is.
Once dough has risen, deflate the dough and divide into 12 equal pieces (~50g each).
Flatten each piece, add a heaping tablespoon of red bean paste to the center, gather the edges and pinch to seal tightly.
Place seam-side down and roll with a rolling pin to slightly flatten the dough, to about 9cm in diameter.
Using a sharp knife or bench scraper, cut 5 slits, making 5 petals, leaving a gap in the center intact.
Cover and let the buns rise in a warm location until puffy and almost doubled in size.