Preheat the oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish.
Place the sweet potato chunks in a large pot of water and bring to a boil. Reduce the heat and simmer for about 15 minutes, or until fork-tender. Drain and return to the pot.
Add milk, maple syrup, butter, cinnamon, nutmeg, vanilla, and salt to the warm potatoes. Mash until smooth and creamy.
Gently stir in 1 cup mini marshmallows. They’ll melt slightly into the potatoes.
Spread the mixture evenly into the prepared pan.
In a medium bowl, combine crushed Jackson’s Sweet Potato Chips with the melted butter. Sprinkle evenly over the top of the casserole.
Bake uncovered for 25–30 minutes, or until the casserole is bubbly and the topping is golden and crisp.