Using a stand mixer fitted with a paddle attachment or a large bowl, combine the potato flakes, salt and sugar. In a medium microwave safe bowl, heat water and butter until butter has melted, about 1 minute. Stir in the milk. With the mixer on low or with a wooden spoon, add the liquid all at once and blend/stir until flakes are moistened (mixture will look crumbly).
Start by kneading ¼ cup of flour into the potato mixture, then add 1/4 cup of flour at a time until the dough clings to the hook and cleans the sides of the bowl or if kneading by hand, the dough should be slightly sticky, but smooth and elastic.
Place dough on a lightly floured work surface. Roll into a log-shaped roll about 2 inches in diameter. Cut log into 16 pieces. (Cutting the dough into 16 pieces will yield a 10 inch lefse round.) Place the dough pieces onto a cookie sheet and refrigerate until ready to use.
Preheat a lefse griddle between 450ºF-475ºF. Generously massage some flour into a covered lefse board or pastry cloth. Remove one dough ball from the refrigerator, roll it into a ball, then flatten the ball on the board with your hand. Using a "sock"-covered, grooved rolling pin, roll out the dough. (For each rolling stroke, rotate the dough so that the dough rolls out evenly into a round shape.) When the dough is half of the desired diameter, use the lefse stick to gently release it from the board and turn over, adding flour to the board and pin as needed.
When the lefse dough is as thin as you would like (you should be able to see the stick through the dough), use the stick to lift the dough and lay it out on the heated and ungreased griddle. Cook the lefse on the first side until it is lightly freckled with light brown spots. Using the lefse stick, turn the dough to the second side and cook until it is spotted with brown spots.
When the lefse is finished cooking, slide the stick under the middle to lift it off the griddle. Lay it on a smooth cotton towel (I use a thin bar towel). Fold the lefse in half and then fold it again in quarters. Cover the lefse with another clean towel to keep the lefse moist while cooling. Repeat with the remaining lefse dough, gently overlapping the finished lefse quarters. Allow the lefse to cool completely before storing. Store in the refrigerator, covered until ready to use. Bring to room temperature before serving. To freeze lefse, place a sheet of wax paper between each quarter, wrap 4-6 lefse in a sheet of plastic wrap and place in a freezer-safe bag or use a vacuum sealer.