Step 1: In a large mixing bowl, combine the chilled chocolate milk and the sweetened condensed milk. Whisk vigorously for 2 minutes until the mixture is completely smooth and the condensed milk is fully incorporated.
Step 2: Gently fold in the thawed whipped topping using a spatula. Do not over-mix; you want to maintain the airiness of the topping to ensure the frosty recipe remains light.
Step 3: Pour the mixture into a shallow, freezer-safe container. A glass dish works best for even freezing.
Step 4: Place the container in the freezer for approximately 2 hours. At the 2-hour mark, remove it and stir thoroughly with a fork to break up ice crystals.
Step 5: Return to the freezer for another 2-4 hours until it reaches your desired consistency. For a smoother texture, pulse the semi-frozen mixture in a blender right before serving.
Step 6: Scoop into chilled glasses and serve immediately, perhaps with a side of fries for dipping!