01 - Lightly grease a 9x9-inch baking pan with butter or coat with 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, about 3-5 minutes.
03 - Add ube halaya and ube extract to the melted marshmallow mixture. Stir vigorously until fully combined and the mixture achieves an even vibrant purple color throughout.
04 - Remove saucepan from heat immediately. Pour in crispy rice cereal and fold gently with a silicone spatula until every piece is evenly coated with the purple marshmallow mixture.
05 - Transfer the mixture to the prepared baking pan. Using a greased spatula or piece of wax paper, press the mixture firmly and evenly into all corners, creating a uniform layer.
06 - If using, drizzle melted white chocolate over the surface in a zigzag pattern. Immediately sprinkle toasted coconut flakes over the chocolate while still wet.
07 - Allow the treats to cool completely at room temperature for at least 1 hour until set. Cut into 16 equal squares using a sharp knife, wiping the blade clean between cuts for neat edges.