Add flour, and salt. Slowly add water until doughy consistency.
Let sit for up to an hour while you prepare filling.
Peel, chop and boil potatoes.
Strain and add milk, butter, and salt. Mash or mix with your favorite mixer until creamy. Feel free to add herbs, spices, or even cheese for an extra bit of flavor.
On a well-floured surface roll dough out until about 1/8th inch thick. Use a large cup to cut circles out of the dough. For smaller pierogies you can use a biscuit cutter.