01 - Lightly grease a 9x9-inch baking pan with butter or nonstick cooking spray. Set aside for later use.
02 - Place unsalted butter in a large saucepan and melt over low heat, being careful not to brown or burn the butter.
03 - Add mini marshmallows to the melted butter, stirring constantly until completely melted and smooth, approximately 3-5 minutes.
04 - Stir in ube halaya and ube extract, mixing thoroughly until fully incorporated and the mixture achieves a vibrant purple color.
05 - Remove saucepan from heat and immediately fold in crispy rice cereal. Gently stir with a spatula until all pieces are evenly coated.
06 - Transfer mixture to prepared pan. Using a greased spatula or wax paper, press firmly and evenly to distribute contents uniformly.
07 - If desired, drizzle melted white chocolate over the surface and sprinkle with toasted coconut flakes while still warm.
08 - Allow treats to cool at room temperature for at least 1 hour until completely set. Cut into 16 equal squares using a sharp knife.