This recipe is an Ukrainian one of my Great-Grandmothers passed down from the years. They are great with melted butter and sauteed onions, or fry if desired. They can also be frozen between layers of plastic wrap.
For a tender pierogi dough, avoid overworking it. Add water gradually until the dough is stiff but pliable; resting it for 30 minutes will make it easier to roll. For the filling, I recommend replacing 'processed cheese' with a blend of sharp cheddar and cream cheese, or farmer's cheese, for a richer, more authentic flavor. Ensure potatoes are thoroughly mashed and seasoned. Crucially, moisten the edges of your dough circles lightly before folding and sealing firmly to prevent the filling from escaping during boiling. Cook pierogi in batches to avoid overcrowding, which can lower water temperature and cause them to stick. Serve with golden sautéed onions and butter, and consider a dollop of crème fraîche or sour cream for a perfect finish.