Melt a bar of white chocolate or candy melts on 50% power in the microwave or in a bowl over a pot of hot water (bain-marie). Stir the chocolate every 30 seconds until fully melted.
Carefully dip the Oreos in the melted chocolate, covering a few centimeters of the stick to help secure it. You can also spoon the chocolate onto the cookie, either sides, holding it above the bowl so the excess chocolate drips back into the bowl.