Boil sweet potato cubes until tender, then drain and mash in a large bowl. Add ½ cup melted butter, milk, half the brown sugar, beaten eggs, vanilla, cinnamon, nutmeg, and a pinch of salt. Mix until smooth and well combined
In a separate bowl, combine chopped pecans, the remaining brown sugar, all-purpose flour, and melted butter. Mix until the mixture is crumbly
Spread the sweet potato mixture evenly in a baking dish. Sprinkle the pecan topping over the sweet potato layer
Bake in the preheated oven for about 25-30 minutes or until the pecan topping is golden brown
Remove the casserole from the oven and evenly distribute the mini marshmallows on top
Turn on the broiler and place the casserole under the broiler for 1-2 minutes, or until the marshmallows are golden brown. Keep a close eye to prevent burning
Allow the sweet potato casserole to cool slightly before serving
