Preheat oven to 425°F. Using House-Autry Buttermilk Biscuit Mix and water, follow the package directions for making rolled buttermilk biscuits. Allow biscuits to cool completely and cut into 1-inch pieces. Measure out enough pieces to equal 5 1/2 cups (approximately 7 biscuits). Place in a large mixing bowl and set aside.
Reduce oven temperature to 325°F. Generously grease a 2 1/2- to 3-quart soufflé dish; set aside. In a medium saucepan, combine the heavy cream, milk and salt over medium heat. Combine the sugar and cocoa; add to the milk mixture and stir until smooth. Heat until sugar has melted and mixture is warm but not boiling. Remove from heat and quickly add eggs, whisking constantly to prevent them from cooking. Stir in vanilla. Pour mixture over bread. Toss in milk chocolate bits, marshmallows and nuts; mix thoroughly and let it stand at room temperature for one hour.
Pour mixture into prepared dish. Dot top with butter. Bake in a hot water bath until edges are set but center still jiggles slightly, 45 minutes to 1 hour. Cool pudding in pan (it will continue to set as it cools).
