Place the white chocolate chips, butter and half of the condensed milk in a smaller bowl and place into the bowl full of water. Mix until the mixture is smooth, making sure not to let the water mix with the chocolate mixture. Fold in the Oreos, and pour into the prepared pan.
Place the chocolate chips into a smaller bowl, and place in the bowl of hot water. Mix until the mixture is smooth. Pour onto the Oreo layer, and refrigerate for around 1 hour to set.
Remove from the refrigerator and peel the foil away. Cut into squares.
Notes
Total time does not include time in fridge to set.