Over low heat, melt the butter in a saucepan. When the butter gets completely melted, add marshmallows. Stir the marshmallows until completely melted and then turn off the heat.
Stir in the cereal until well coated.
Evenly press mixture in a 13 x 9 pan coated either with cooking spray or lined with parchment paper. (Note: I used the back of a small bowl to press the mixture evenly).
Mix white chocolate morsels and oil in a microwave safe bowl. Microwave the chocolate for 20 seconds and stir well. Repeat the process and check and stir the mixture every 20 seconds until the chocolate is completely melted. Evenly coat the cereal mixture with white chocolate. Sprinkle it with the blue sparking sugar.
Cool for 10 minutes and cut into squares. Best served the same day.