Start by reducing the apple cider. Pour into a medium pot and bring to a boil over high heat. Continue to boil uncovered for 15 minutes to a half hour, depending on how wide your pot is. Remove from heat when the cider has reduced to 1/2 cup liquid.
Refrigerate or freeze the cider until it is completely cool. You can do this ahead of time, it will keep for a long time.
Pour 1 and 1/2 to 2 inches of oil into a high-sided skillet. Set over medium heat and wait at least 5 minutes for the oil to get to frying temperature (between 350 and 375 degrees F.)
Pop the can of biscuits and separate them out. Use your fingers to stretch the dough to about the size of a dollar bill, about 6 inches.
Fry the doughnuts 2 at a time in the hot oil. Fry for about 2 minutes, or until the dough is light brown on the bottom. Flip with tongs, then fry for another 1-2 minutes or until light brown.
Remove to a paper towel lined plate. Repeat with the remaining doughnuts.
Let the doughnuts cool completely. Good luck with this step.
In a medium bowl, whisk together 2 cups of powdered sugar and 3 tablespoons of the reduced apple cider. Mix it all together and add more apple cider to get to a consistency you like. Keep covered until the doughnuts are ready.
Dip one side of the doughnuts into the apple cider glaze. Serve immediately!