Twice-Baked Sweet Potatoes with Bacon, Brown Sugar, and Marshmallows

Preheat oven to 400 degrees F. Prick sweet potatoes all over with a fork and rub with vegetable oil. Season with salt. Bake directly on oven rack until tender, 50 to 60 minutes. Let cool. Meanwhile, in a large skillet over medium heat, cook bacon until crisp, 5 to 7 minutes. Transfer to a paper towel-lined plate to let cool, then crumble 2 slices. Reserve 2 tablespoons bacon fat. When sweet potatoes are cool enough to handle, make a slit in the top and carefully scoop out flesh into a medium bowl. Transfer potato skins to a parchment-lined baking sheet. Mash potato flesh until mostly smooth (or as smooth as you like it). Add crumbled bacon, reserved bacon fat, 1/4 cup brown sugar, and 1/2 teaspoon salt and stir to combine. Increase heat to 425 degrees F. Carefully divide sweet potato mixture among skins and top with remaining 2 tablespoons brown sugar and marshmallows. Tuck remaining bacon into sweet potatoes, breaking into pieces to evenly distribute. Bake until marshmallows are golden brown, 6 to 8 minutes. Dust with cinnamon before serving.