01 - Grease a 9x9-inch baking pan with butter or nonstick cooking spray to prevent sticking.
02 - Melt butter in a large saucepan over low heat. Add marshmallows and stir continuously until completely melted and smooth.
03 - Stir in ube halaya and ube extract until fully incorporated and the mixture achieves a vibrant purple color.
04 - Remove from heat and immediately fold in crispy rice cereal. Gently stir with a spatula until all cereal is evenly coated.
05 - Transfer mixture to the prepared pan. Using a greased spatula or wax paper, press firmly and evenly into the pan.
06 - Drizzle melted white chocolate over the top and sprinkle with toasted coconut flakes if desired.
07 - Let cool at room temperature for at least 1 hour, then cut into 16 squares.