Preheat the oven to 400°F (200°C). Prick the sweet potatoes a few times with a fork to allow steam to escape while baking.
Bake the potatoes directly on the rack or on a foil-lined baking sheet for 40–50 minutes, or until they’re very tender when pierced with a knife.
While the potatoes bake, melt the butter in a small skillet over medium heat. Add the brown sugar, cinnamon, and salt; cook for 1–2 minutes until the mixture is bubbling and fragrant. Stir in the maple syrup if using and remove from heat.
Toast the chopped pecans in a dry skillet for 2–3 minutes until fragrant, then toss them with the melted butter mixture to coat.
When the potatoes are done, let them cool for a few minutes. Slice each potato lengthwise, careful not to cut all the way through. Fluff the inside with a fork, then swirl in a teaspoon of butter and a splash of vanilla.
Fill each potato with the pecan-brown sugar mixture, pressing the filling into the crevices. Reserve any leftover pecan mixture for topping.
If desired, top with mini marshmallows and return to the oven for 4–6 minutes, or until the marshmallows puff and lightly brown. Remove from the oven and finish with a light drizzle of extra maple syrup if you like an extra gloss.
Serve warm. The sweet, creamy interior paired with the crunchy pecan topping makes every bite feel cozy and celebratory.