In a food processor, pulse the Oreo cookies until they turn into crumbs. You will probably have to do this in 2 or 3 batches depending on size of food processor. Pour the Oreo crumbs in a large mixing bowl.
Melt the white chocolate chips in a microwave safe bowl for about 30-45 seconds or until melted. Stir to make sure all the chips are completely melted.
Pour the condensed milk into the bowl with the chocolate chips and stir until smooth. Pour 1/4 cup of rainbow sprinkles into the mixture and stir again.
Pour the chocolate chips mixture into the bowl with the Oreo crumbs. Stir to mix all together.
Pour the mixture into the prepared pan. Using a spatula, smooth out the top. Add the remaining sprinkles on top and gently press down with the spatula so they stick.
Cover the pan and place in the refrigerator to chill for at least 2 hours.
Remove from the refrigerator, cut into small squares and serve. Enjoy these cake truffles! Want to freeze leftovers? Place them in a freezer bag and freeze until ready to eat. Frozen cake batter truffles will last in the freezer for 2-3 months.