Grease a 13 x 9 x 2 baking dish with cooking spray or butter.
Melt butter in a large saucepan at low to medium-low heat.
Add marshmallows slowly, stirring as they melt.
Stir in the rice cereal until well coated.
Press mixture into the prepared pan using wax paper or a buttered spatula.
Let cool to room temperature.
Cut into 3 inch squares.
Heat a few inches of water in a double boiler (or use a medium saucepan for water with small saucepan for the chocolate) until boiling.
Add the coconut oil and white chocolate chips while continuously stirring as they melt.
Once melted, dip each rice krispie treat until half covered with melted white chocolate.
Set on wax or parchment paper and add sprinkles before the white chocolate hardens.