Peel the sweet potato and cut it into 1-inch cubes on a cutting board.
Cover the sweet potato cubes in a medium saucepan with cold water. Bring to a boil. Reduce the heat, and simmer for 15 minutes or until very tender.
Drain the potatoes using a colander and cool slightly.
Place potatoes in the bowl of a stand mixer (or medium bowl and hand mixer).
Add the brown sugar, butter, salt, and vanilla and mix until mashed and well combined.
Fold in 1 tablespoon chopped pecans.
Coat an 18.6 oz oven-safe baking dish with nonstick cooking spray.
Scoop the mashed sweet potatoes into the dish in an even layer.
Sprinkle with the remaining 1 tablespoon chopped pecans.
Top with marshmallows and bake for 15 minutes or until golden.
Video
Notes
Store leftovers in an airtight container in the fridge for 4-5 days. To freeze this cooked sweet potato casserole, let it come to room temperature, then store it in a sealed container or freezer bag.
You can use canned sweet potatoes instead of fresh sweet potatoes. Use about 8 ounces or 1 cup of canned.
You can make this a nut-free version by omitting the pecans.
Use light brown sugar or dark brown sugar.
If you want to serve individual portions you can make two mini sweet potato casseroles using two 10-ounce ramekin dishes.
If you have large marshmallows cut them into smaller pieces for this recipe.