Western desserts - Sweet potato casserole

Recipe ingredients:

5 large sweet potatoes

1/4 cup butter

A pinch of salt

1/4 spoon of cinnamon

1/4 teaspoon nutmeg

1/2 cup cream

3 tablespoons brown sugar

Crunchy walnut layer:

1 cup raw walnuts

2 tablespoons brown sugar

1/2 teaspoon salt

3 tablespoons toasted oats

Marshmallow for face