Brew the milk tea – Make a strong cup of black tea, mix in milk and a pinch of salt. Sweeten lightly if you like. Let it cool.
Prepare the dough – In a bowl, mix glutinous rice flour and sugar. Slowly pour in cooled milk tea. Stir until a soft dough forms. Add more tea a little at a time if needed.
Make the filling – Mix softened butter with sweetened condensed milk until smooth and creamy.
Shape the balls – Take a small piece of dough, flatten it, and place a small spoon of filling in the center. Wrap the dough around the filling and roll into a smooth ball. Repeat with remaining dough.
Coat the balls – Roll each ball in toasted sesame seeds or crushed nuts. Dust with powdered sugar if desired.
Chill or serve – Place balls on a tray and refrigerate for 30 minutes. Serve slightly chilled with milk tea or bubble tea.