Twist the Oreo cookies apart so that you have two halves.
Arrange them on the parchment lined baking sheet.
Add the white chocolate chips to a microwave safe bowl, and heat in 30 second intervals, stirring between each heating session, until fully melted.
Immediately pour melted chocolate over cookies, slowly, starting in the middle, and moving to the sides. Use the spoon to help spread it across all of the cookies.
Immediately top with M&Ms.
Transfer the entire pan to the refrigerator, and chill for one hour.