Place the sweet potatoes on a foil-lined baking pan. Bake until a paring knife inserted in the center pierces easily, about 1 hour. Cool slightly.
Meanwhile, cook the bacon in a medium skillet over medium heat until crisp and brown, about 7 minutes. Transfer to a paper-towel lined plate to drain. Reserve 1 tablespoon of the bacon fat. Crumble bacon.
Halve the sweet potatoes lengthwise. Carefully scoop most of the flesh out into a bowl, leaving enough flesh in the skin so that it holds its shape. Add the bacon, bacon fat, scallions, maple syrup and 1 cup of the cheese to the sweet potato flesh. Stir together and season with salt and pepper to taste. Refill the sweet potato shells and sprinkle with the remaining cheese.
Place the sweet potatoes back in the oven until heated through and the cheese is melted, about 15 minutes. Top with the reserved scallions and dollops of sour cream.