The method my grandmother prepared it was quite cruel. You put the turtle in a big stock pot, half filled with cold water. Gradually bring it to a boil. Make sure to put some heavy weight on top of the lid to prevent the turtle from getting out. As the water warms up, the turtle will get rid of its excrement. When it is dead, crack the shell and get rid of the internal organs but save the liver and heart. Chop the meat into large (2 to 3 inches cube) pieces, rinse well, and put it into a pot or double steamer with shitake mushrooms or Chinese herbal roots, a dash of rice wine, and simmer or steam for several hours. Another slightly more "humane" method was to bait the turtle with some meat stuck on a chopstick. When it stick its head out to take the meat, chop its head off immediately with a sharp cleaver. I have only heard of this method and never seen it done. Personally I will stick with frozen turtle (if it is available) and let some body else do the dirty work.