1. In a mixing bowl, whisk together the glutinous rice flour, granulated sugar, milk, and mango puree until smooth and lump free.

2. Pour the mixture into a heatproof bowl and steam for 20 to 25 minutes, or microwave in short intervals, stirring between each interval, until the dough becomes thick, glossy, and stretchy.

3. Add the unsalted butter to the warm dough and fold until fully incorporated and smooth.

4. Dust a tray or plate generously with cornstarch or potato starch, transfer the dough onto it, and let it cool.

5. Chill the dough for 20 to 30 minutes until easier to handle.

6. Peel and cut the ripe mango into small cubes, keeping the pieces small enough to fit inside each mochi.

7. Dust your hands and work surface with more starch, then divide the dough into 8 equal portions.

8. Flatten each portion into a round wrapper, keeping the center slightly thicker than the edges.

9. Place a piece or spoonful of mango in the center of each wrapper.

10. Gather the edges, pinch to seal, and gently roll into a smooth ball with the seam underneath.

11. Lightly dust the finished mochi with more starch or powdered sugar if desired.

12. Serve slightly chilled or at cool room temperature.