Preheat the oven to 450 degrees F. Place the sweet potatoes on a baking sheet and bake for 1 hour, or until very fork tender. (This can be done up to 3 days ahead. Refrigerate the baked sweet potatoes if making ahead.)

Change the oven temperature to 350 degrees F.

Set out a large mixing bowl. Peel the loose skins off the hot baked sweet potatoes. Place them in the bowl. Add the butter, brown sugar, salt, cinnamon, and vanilla extract. Use an electric mixer to beat the sweet potatoes into a smooth mash.

Set out a 9X 13 inch baking dish. Scoop the sweet potato mash into the dish, and spread it out in an even layer.

Sprinkle the chopped pecans on top. Then sprinkle the mini marshmallows over the pecans in a single layer.

Bake for 20-25 minutes, until the marshmallows are golden and puffy. Serve warm.