1) Combine 2 cups of milk and the doughnut in a blender, and blend on high speed until the doughnut is completely blended into the milk. Depending on your blender, this may take up to a minute.
2) Pour the milk through a strainer into a saucepan to catch any remaining doughnut bits, then place the pan over medium heat. Bring the milk to a low simmer and whisk until it thickens, about 2-3 minutes. (The flour in the doughnuts will cause the milk to have a wonderfully thick creamy texture.)
3) Add the chopped semi-sweet chocolate and the salt, and whisk constantly until the chocolate melts and the liquid is smooth. If desired, whisk in the remaining 1/2 cup of milk for a thinner, more drinkable consistency.