Preheat your oven to 375°F and grease a 9x13-inch baking dish.
Bring a large pot of water to a boil. Add the sweet potato cubes and cook for 8-10 minutes until they're tender but still hold their shape. Drain well.
In a large bowl, whisk together melted butter, brown sugar, maple syrup, vanilla extract, cinnamon, nutmeg, and salt.
Add the drained sweet potatoes to the bowl and gently toss to coat everything in that delicious sweet mixture.
Transfer the sweet potatoes to your prepared baking dish, spreading them out evenly. Pour any remaining syrup from the bowl over the top.
Cover the dish with foil and bake for 30 minutes, stirring once halfway through.
Remove the foil and sprinkle the mini marshmallows evenly over the top. Return to the oven, uncovered, for another 10-15 minutes until the marshmallows are golden and perfectly toasted.
Let it cool for about 5 minutes before serving (if you can wait that long!).