Rinse and soak kidney red beans thoroughly.
Boil the soaked beans until cooked, then drain in a sieve.
Add sugar and salt to the boiled beans and simmer over medium heat to make sweet red bean paste.
Mix bread flour, yeast, sugar, salt, milk, and butter to make the dough.
Let the dough rise for the first proof.
Divide the dough and shape into balls.
Flatten each ball, add the red bean paste, and shape into a round bun.
Place the buns on a pan and let them rise for a second proof.
Bake in a preheated oven at 180°C (356°F) for 15 minutes.