In pot, boil potatoes in water until tender when pierced by a sharp knife. Drain and cool completely. Peel and rough chop potatoes. Dissolve yeast in the warm water and let sit for 10 minutes. In food processor, combine the flour and salt. Cut in the butter by pulsing the processor 8 or 9 times, then add the potatoes. Process briefly until you have a soft dough. Or in large bowl combine the flour and salt, cut in the butter with a pastry cutter or 2 knives. Add the potatoes with a wooden spoon until you have a soft dough.
Remove the dough to a floured work surface, pat out and shape the dough into a 8x12" rectangle. Fold in thirds as you would a letter. Cover loosley and chill for 2 hours.
Remove from refrigerator and roll out again into 8x12" rectangle. Fold again into thirds and chill for 24 hours.
Roll out again, fold again and chill 2 more hours.
Roll out the dough into 9x15" rectangle, about 1/2" thick. With sharp knife, cut the dough into forty-five 1x3" rectangles.(Make 8 lengthwise cuts 1" apart, and 4 crosswise cuts 3" apart). Place them on a lightly greased baking sheet. Let rise again for 20-25 minutes. Meanwhile, pre-heat oven to 400 degrees F. Brush the biscuits with the beaten egg wash and bake for 16-18 minutes or until golden brown.
After biscuits have cooled completely, you can freeze the extras for another time.