01 - Lightly grease a 9x9-inch baking pan with butter or nonstick cooking spray to prevent sticking.
02 - Place butter in a large saucepan over low heat. Once melted, add mini marshmallows and stir continuously until completely melted and smooth.
03 - Add ube halaya and ube extract (if using) to the marshmallow mixture. Stir thoroughly until fully incorporated and the mixture achieves a vibrant purple color.
04 - Remove saucepan from heat. Immediately add crispy rice cereal and fold gently with a spatula until all pieces are evenly coated with the purple marshmallow mixture.
05 - Transfer the mixture to the prepared baking pan. Using a greased spatula or wax paper, press the mixture firmly and evenly into the pan corners.
06 - If desired, drizzle melted white chocolate over the surface and immediately sprinkle with toasted coconut flakes while chocolate is warm.
07 - Allow treats to cool at room temperature for at least 1 hour until completely set. Cut into 16 equal squares using a sharp knife.