Set aside 8 ounces of white candy melts in a small, microwave-safe bowl.
Add the rest of them to a large, microwave-safe bowl and melt in 30-second intervals.
Add the OREO pieces to the large bowl of melted chocolate and stir gently to coat.
Scoop the melted chocolate with coated OREOS onto the baking sheet and spread evenly.
Melt the 8 ounces of chocolate that you previously set aside.
Break up about 4-5 more OREOS into coarse pieces for the topping.
Pour about 7 ounces of the melted chocolate over the top of the mixture that’s on the baking sheet.
Add the broken OREO pieces to the top of the bark and sprinkle on the M&Ms.
Drizzle the remaining amount of melted chocolate on top of the cookies and candies.
Set the baking sheet into the refrigerator for at least 15 minutes to harden.
Remove the sheet and break the bark candy with your hands or cut it into pieces.