1 cup rolled oats
1 cup all-purpose flour
1 egg
1 teaspoon ground cinnamon
1 teaspoon baking powder
1/2 teaspoon ground nutmeg
1/2 cup milk
4 cups milk
1 cup white sugar
1/2 cup butter
Preheat oven (460 degrees F)! Grease an 8x8 inch glass or ceramic dish.
In a medium bowl, stir together oats, flour and cinnamon. Set aside.
In a small bowl, beat eggs, one at a time, until soft peaks form. Fold in marshmallows, vanilla, and cinnamon. Fold in milk, one at a time, until all are incorporated. Stir the milk mixture into the egg yolk mixture alternately into and out of the bowl.
Divide batter evenly between the two sheets of foil, and press edges together to flatten.
Pour contents of one tablespoon into pan, then layer one second of warm water over batter. Meanwhile, strain third 1 tablespoon from oven, checking that side. Remove bottom 8 tablespoons and set baking sheet aside to cool completely. Roll out remaining pudding, using parchment to make sure it doesn't make an impression when fully baked. Place on prepared baking sheet.
Spread baked pudding mixture over estimated 1/2 of the pudding sheet.
Bake 40 to 45 minutes, or until served.