Prep Your Station. To start, line two baking sheets with parchment paper and set aside. Set out all toppings you plan to add to the Oreos and have them ready to add as soon as the chocolate is melted. Make sure all your bowls and tools are clean and totally dry before starting.
Melt Chocolate. In a small microwave-safe bowl, gently melt chocolate candy melts in 15-2o second intervals, stirring the chocolate in between each interval until the chocolate is smooth, glossy, and fully melted. (16 oz. of candy melts will be enough to coat a package of Oreos. You can decide if you'd like to do all dark chocolate or make half dark chocolate and half white chocolate. Use separate bowls for dark and white chocolate.)
Dip Oreos. Add an Oreo cookie to the melted chocolate and use a fork or chocolate dipping tool to gently turn the Oreo until it's coated completely in chocolate. Lift the dipped Oreo out of the chocolate and tap the fork gently against the side of the bowl to allow any excess chocolate to drip back into the bowl. (You may also need to wipe the bottom of the fork against the edge of the bowl to remove extra chocolate.) Place the chocolate-dipped Oreo on a parchment-lined baking sheet.
Decorate Quickly. Add any desired toppings (such as sprinkles or candy cane) while the chocolate is still wet and glossy. If you're planning to drizzle them with additional chocolate later, let the cookies set completely before drizzling with the next layer of chocolate.
Repeat this process until all the Oreos are dipped in chocolate. If the chocolate starts to set up or thicken, pause to re-heat the chocolate for 10-15 seconds at a time until it becomes melted and easy to work with again. You can also use a separate bowl to melt white candy melts to dip some of the cookies or drizzle on later.
Let Cookies Set. Let the Oreos set up completely before storing or serving. (The chocolate will go from shiny to matte.)
Drizzle, If Desired. If you'd like to add a chocolate drizzle to the Oreos, use extra melted chocolate to drizzle onto the set Oreos. If desired, add sprinkles or toppings on top of the chocolate drizzle. Let cookies set before storing.
Serve & Store. Enjoy right away or store leftovers in an airtight container for up to 2 weeks.