01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - Pierce sweet potatoes several times with a fork. Arrange on the prepared baking sheet and bake for 40 to 45 minutes, or until fork tender.
03 - Remove sweet potatoes from the oven. Let them cool slightly, then cut each potato in half lengthwise.
04 - Carefully scoop out most of the flesh, leaving a 1/4-inch border inside each skin. Transfer the flesh to a mixing bowl.
05 - Mash the sweet potato flesh with melted butter, ground cinnamon, sea salt, and brown sugar until smooth. Stir in shredded cheddar cheese and chopped pecans, if using.
06 - Spoon the prepared filling back 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.
07 - In a small saucepan over low heat, melt mini marshmallows with milk, stirring continuously, until the mixture is smooth and pourable.
08 - Remove sweet potato skins from the oven. Drizzle with the melted marshmallow mixture. Sprinkle with chopped chives and flaky sea salt.
09 - Present warm for optimal texture and flavor.