Take 1 tablespoon of the butter and add to a small fry pan, then saute the white parts of the scallions until soft. In a large sauce pot, boil the potatoes until they are tender. Drain the potatoes well, add the sauteed scallions, then mash and whip in butter, salt and white pepper, to taste, with a beater. Fold the cheese into the potatoes and allow it to melt. Stir to evenly distribute cheese, transfer to a serving dish and garnish with finely chopped tender green parts of scallions or fresh chives.