Preheat oven to 350 degrees. Grease a 9x13 pan with butter. In a large mixing bowl, stir together the cocoa and melted butter. Add the eggs, flour, sugar, salt, and vanilla. Beat well and pour into prepared pan. Bake for 30-35 minutes.
Icing:
Beat the brown sugar and butter. Add the cocoa and mix well. Stir in the scalded milk and vanilla until smooth. Pour the marshmallows over the cake while still hot and then immediately pour the frosting over the marshmallows. Let cool before cutting.