3 pounds small Yukon Gold or Yellow Finn potatoes, scrubbed
2 bunches of scallions, white and tender green, cut into 1/2-inch pieces
2 teaspoons salt
1 1/2 cups mascarpone cheese (about 3/4 pound), at room temperature
1/4 cup finely chopped flat-leaf parsley
Freshly ground white pepper
Using small unpeeled boiling potatoes saves a great deal of time; the skins of Yukon Golds are particularly tender. If you don't like the skins, use larger baking potatoes and peel and quarter them.