In a microwave-safe mixing bowl, melt the butter. Stir in the cocoa and let the mixture cool. When cool, stir in the sugar, flour and salt and mix with a wooden spoon. Crack in the eggs, one by one and beat with the spoon, then beat in the vanilla until the mixture is well-blended. Pour into the pan and bake for 20 minutes or until top appears set. Remove from the oven and let cool for about 10 minutes. Warm peanut butter for 10 seconds in the microwave and spread it over the brownies. Sprinkle marshmallows, chocolate chips and peanuts over the peanut butter layer. Return the oven and bake for 3-4 minutes or just until marshmallows puff up. Let cool at room temperature. If desired, melt some milk or dark chocolate in the microwave using 50% power. Drizzle melted chocolate over the rocky road topping. Let cool completely, then put in the refrigerator. When chilled, lift from pan and cut into 16 squares.