Preheat the oven to 400°F and gather ingredients. Line a sheet pan with foil, and place the sweet potatoes on it. Prick them with a fork, and then bake for 40-50 minutes, depending on their size. Test with a fork to ensure they're done.

Lower the oven temperature to 350°F and let the sweet potatoes cool for at least 20 minutes. Meanwhile, in a bowl, whisk together the sugar, butter, milk, vanilla, and salt.

Peel the sweet potatoes and add them to the bowl. Stir and mash everything together to combine. Stir in the eggs.

Spread the mixture into a small 20-ounce (0.6L) baking dish and bake for 20 minutes.

Remove the baking dish, scatter the marshmallows on top, and bake for another 5-10 minutes, until the marshmallows toast and become lightly golden brown. Serve immediately.