Since these potatoes are "hasslebacked," or sliced accordion-style, before baking, the scallions and bacon fat really penetrate; the sour cream and bacon are the icing on the cake. (The dish has been known to elicit marriage proposals from strangers and tears from bacon lovers.)
Cooks' notes:
·Potatoes can be roasted on a grill prepared for indirect-heat cooking over medium-hot charcoal (moderate for gas).
·Sour-cream topping, without crumbled bacon, can be made 2 hours ahead and chilled, covered. Just before serving, crumble bacon over topping.
