01 - Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
02 - Pierce sweet potatoes several times with a fork. Arrange on the prepared baking sheet and roast for 40 to 45 minutes, until tender.
03 - Remove from oven and let cool slightly. Cut each potato in half lengthwise. Carefully scoop out most of the flesh, leaving a 1/4-inch border to maintain skin structure.
04 - In a mixing bowl, combine the scooped sweet potato flesh, melted butter, ground cinnamon, sea salt, and brown sugar. Mash until smooth. Mix in shredded cheddar cheese and pecans if desired.
05 - Spoon the prepared filling into the sweet potato skins, mounding slightly. Return filled skins to the baking sheet and bake for 10 minutes, until heated through and cheese is melted.
06 - While skins bake, melt mini marshmallows with milk in a small saucepan over low heat, stirring constantly until smooth and pourable.
07 - Remove sweet potato skins from the oven. Drizzle generously with the marshmallow mixture. Sprinkle with fresh chives and flaky sea salt.
08 - Serve sweet potato skins warm for optimal texture and flavor.