Preheat your oven to 350°F (175°C).
Peel and cut the sweet potatoes into chunks.
Boil the sweet potatoes until fork-tender, approximately 15-20 minutes.
Drain and transfer the sweet potatoes to a mixing bowl.
Mash the sweet potatoes until smooth.
Mix in granulated sugar, brown sugar, milk, melted butter, eggs, and vanilla extract.
If desired, fold in half of the chopped pecans.
Transfer the mixture to a greased baking dish, spreading it evenly.
Top with remaining pecans (if using) and mini marshmallows (if desired).
Bake in the preheated oven for 25 to 30 minutes, until heated through and topping is golden.
Remove from oven and let it cool for a few minutes before serving.