- Sweet Potato Base:
- 10 sweet potatoes, peeled and cut into chunks
- 3/4 cup brown sugar
- 1/2 cup heavy whipping cream
- 1/4 cup melted butter
- 1/4 teaspoon ground cinnamon
- 1/4 teaspoon salt
- Oatmeal Topping:
- 1/4 cup rolled oats
- 2 tablespoons dark brown sugar
- 1 tablespoon all-purpose flour
- 1/8 teaspoon ground cinnamon
- 2 tablespoons cold butter
- 2 cups miniature marshmallows
- Preheat oven to 400 degrees F (200 degrees C).
- Spread sweet potatoes onto baking sheets in a single layer.
- Roast sweet potatoes in preheated oven until tender, about 1 hour. Cool potatoes completely before mashing with a potato masher until smooth.
- Measure 6 cups mashed sweet potato into a large mixing bowl. Reserve remainder of sweet potato for another use. Stir 3/4 cup brown sugar, heavy cream, melted butter, 1/4 teaspoon ground cinnamon, and salt with the mashed sweet potato until smooth; spread into an 8-inch square baking dish.
- Mix oats, 2 tablespoons dark brown sugar, flour, and 1/8 teaspoon cinnamon together in a bowl. Cut butter into the oats mixture until crumbly in consistency; spread over the top of the sweet potato mixture to cover.
- Bake in preheated oven until the top begins to brown slightly, about 1 hour. Spread mini marshmallows over the top of the casserole, turn oven off, and let casserole sit in oven until the marshmallows are melted and slightly browned, about 10 minutes.