Prepare an 8-inch square pan by rubbing liberally with butter; set aside.
Place milk, water, sugar, and butter into a large saucepan. Bring to a boil over medium heat, stirring continuously. Turn heat to low, and continue to simmer until a candy thermometer reaches 234 to 240 degrees F (112 to 116 degrees C), or until a small amount of syrup dropped into cold water forms a soft ball that flattens when removed from the water and placed on a flat surface, about 10 minutes.
Once the temperature has been attained, and the tablet has turned a dark tan color, remove from heat, and let stand for 5 minutes.
Beat tablet with an electric hand mixer for five minutes, until it cools and begins to harden. Pour into prepared pan, and score into serving-size pieces while it is still soft. Allow to cool until completely set, 6 hours to overnight.
