Step 1: Preheat your oven to 400°F (200°C). Prepare a large baking sheet by lining it with parchment paper for easy cleanup.
Step 2: In a large bowl, combine the melted butter, brown sugar, vanilla extract, ground cinnamon, and salt. Whisk until the sugar is dissolved and the mixture is well combined.
Step 3: Add the cubed sweet potatoes to the bowl with the brown sugar mixture. Toss well until all the sweet potato cubes are evenly coated.
Step 4: Spread the coated sweet potato cubes in a single layer on the prepared baking sheet. Ensure they are not overcrowded; use a second baking sheet if necessary to allow them to roast rather than steam.
Step 5: Roast for 20-25 minutes, stirring gently halfway through, until the sweet potatoes are tender and their edges begin to caramelize. They should be fork-tender.
Step 6: Remove the baking sheet from the oven. Evenly sprinkle the mini marshmallows and chopped pecans over the roasted sweet potatoes.
Step 7: Return the baking sheet to the oven and bake for an additional 3-5 minutes, or until the marshmallows are puffed, golden brown, and gooey. Watch carefully to prevent burning.
Step 8: Remove from the oven and let cool slightly before serving. The caramel and marshmallows will be very hot.