Sweet Potato Casserole

3 tbsp unsalted butter, cut into 1 inch pieces
3 1/2 lbs sweet potatoes, peeled, quartered, and cut crosswise into 1 inch pieces
1/2 cup packed brown sugar
1 teaspoon salt
1/4 teaspoon pepper
1/2 cup water
2 cups mini marshmallows

Directions:

Preheat oven to 375 degrees
Melt butter in Dutch oven over medium high heat. Stir in sweet potatoes, sugar, salt pepper and water and bring to a simmer. Cover, reduce heat to medium-low, and cook, stirring often, until potatoes are completely tender, 35 to 45 minutes. Off heat, mash sweet potato mixture with potato masher until smooth (my dad likes his chunky)
Transfer potato mixture to 13 by 9 inch baking dish. Top with marshmallows and bake till marshmallow melt and are browned.