Peel and cut potatoes. Boil in well salted water until soft. Use more salt than you normally would. You do not want to add salt once they are cooked as it will not dissolve as well.
Drain well and return to pot. Steam for a few minutes to ensure all water has been evaporated.
Measure out 4 cups of potatoes, packed well. Rice potatoes now while potatoes are still hot. You may have potatoes left over.
Place riced potatoes in a plastic bowl with a good sealing lid. Add butter and milk and mash with a HAND masher. Do NOT use an electric mixer as it will get sticky.
Allow to cool on the counter until potatoes are at room temperature then place several paper towels on top, seal tightly with the lid and place in the refrigerator overnight.
Next day: Much easier to work with. Mix in flour and sugar and form into small balls. Now roll them out thin and flat using a rolling pin, preferably one with grooves and covered with a sock. You can just cut an old CLEAN sock and slide it over the rolling pin.
Using a lefse stick or a long flat stick or long thin spatula roll the raw lefse around the stick and then unroll onto a HOT griddle (450 degrees) Flip once the first side starts to form bubbles and is lightly browned or freckled. Cook other side just until lightly browned.
Using stick again remove lefse from griddle to a towel and place a towel on top to keep them warm and pliable.
Eat warm or store in the refrigerator in a well sealed container lined with more paper towels. Can also be frozen with waxed paper between each lefse.