Place the cubed sweet potatoes in a microwave-safe bowl and add enough water to cover the potatoes. Cook on high for 10-15 minutes until tender and then drain. (This step can be done on the stovetop if you prefer)
Add the granulated sugar, whole milk, melted butter, eggs, vanilla, and salt in a bowl and beat until smooth. Spread in a greased, casserole dish.
Bake at 350˚F for 30-35 minutes until heated through.
Top with the marshmallows. Broil for 1-2 minutes until golden brown.
Video
Notes
Make Ahead
You can prepare this recipe ahead of time and store it in the refrigerator. Place it on the counter while preheating the oven. Then, bake as directed.