To prepare the sweet stiff starter, mix the active starter, bread flour, water, and sugar into a stiff dough. Let it rise until tripled in size.
To make the tangzhong, combine the bread flour and milk in a saucepan and cook until thick. Remove from heat and allow it to cool completely.
In a stand mixer, combine the pineapple juice, egg, sugar, tangzhong, sweet stiff starter, bread flour, and salt. Mix until combined, then let the dough rest for 20–30 minutes.
Begin kneading the dough, then gradually add the butter. Continue mixing until the dough becomes smooth, elastic, and slightly tacky, and passes the windowpane test.
Cover the dough and let it bulk ferment at a warm room temperature for 4–6 hours. The dough should rise slightly, about 30%, but not double.
Divide the dough into 12–15 portions, about 80–85g each. Shape each portion into a tight ball and place into a baking pan.
Allow the dough to proof at room temperature for 2–4 hours, or refrigerate overnight. The rolls should become puffy and begin touching.
Preheat the oven to 350°F (175°C). Brush the rolls with egg wash before baking, then bake for 20–25 minutes.
Remove from the oven, brush with butter, and sprinkle with sugar.