Preheat oven to 350°.
Grease a 13x9x2-inch pan.
Stir 1/2 cup cocoa into mixing bowl with 1 cup butter.
Add eggs, flour, sugar, salt and 1 teaspoon vanilla.
Beat well with a mixer.
Fold in nuts.
Pour into prepared pan and bake for 35 minutes.
While cake is baking, prepare frosting.
Scald the milk.
Beat the brown sugar and 1/4 cup butter together.
Add 1/3 cup cocoa, milk and 1 teaspoon vanilla and beat until smooth.
Remove cake from oven when done and pour marshmallows over hot cake.
Pour frosting over marshmallows on top.