Make the dough: Mix yeast with warm water and let it foam. Add flour, sugar, and salt, then knead until smooth. Let it rise for 1-2 hours.
Make the filling: Cook chicken with garlic, ginger, soy sauce, and pineapple until well combined. Let it cool.
Prepare the topping: Mix butter, sugar, egg yolk, flour, and baking powder into a dough. Roll into small balls.
Assemble the buns: Flatten dough, add the filling, seal the bun, and top with the pineapple crust.
Bake: Preheat the oven to 350°F (175°C) and bake for 15-20 minutes until golden.
Serve: Let cool slightly and enjoy.