How to Make It
Preheat the oven to 400°. Prick the potatoes all over with a fork and put them on a rimmed baking sheet. Brush with olive oil and season with salt. Bake the potatoes for about 1 hour, until tender.
Meanwhile, spread the pecans in a pie plate and toast in the oven until golden and fragrant, about 7 minutes. Let cool, then coarsely chop.
In a medium saucepan, combine the orange juice with the honey and brown sugar and bring just to a boil, stirring to dissolve the sugar. Let the honey syrup cool.
In another medium saucepan, combine the granulated sugar with the corn syrup and water and cook over moderate heat, stirring occasionally, until the sugar syrup registers 240° on a candy thermometer.
In a stand mixer fitted with the whisk, beat the egg whites with the cream of tartar at medium speed until soft peaks form. Turn the machine to medium-high and drizzle the hot sugar syrup into the egg whites in a very thin stream down the side of the bowl; beat until stiff peaks form and the marshmallow is cool. Scrape the marshmallow into a pastry bag fitted with a medium straight tip.
Cut off and discard the ends of the warm potatoes, then cut them crosswise into 2- to 3-inch sections. Arrange on a platter. Spoon some of the honey syrup over the potatoes and on the platter. Pipe the marshmallow topping onto the potatoes and, using a kitchen torch, lightly toast the tops. Alternatively, you can pipe the marshmallow onto a greased foiled-lined baking sheet and broil, then use a cake spatula to transfer onto each sweet potato section. Sprinkle the pecans over the top and serve.