Cut the passion fruits in half and scoop out the pulp into a bowl. Press the pulp through a fine sieve to extract about 100-120 ml of juice, discarding the seeds and solids.

Dice the ripe mango flesh into small pieces and blend until smooth.

In a medium-sized saucepan, combine the extracted passion fruit juice, mango puree, sugar, and mizuame. Place the pan over low heat, stirring until the sugar and syrup dissolve.

Gradually add the cornstarch dissolved in water while stirring rapidly. Bring the mixture to a simmer over medium heat until it thickens.

Reduce heat to low, add the butter, stir continually until it melts and integrates into the mixture.

Prepare a baking tray by lining it with parchment paper. Pour the thickened mixture into the tray, spreading it evenly. Let it cool at room temperature for 1-2 hours until set.

Once set, lift the parchment paper and cut the candy into squares or rectangles, rolling in granulated sugar if desired.