Preheat oven to 325 degrees
Grease a 9 x 13 inch baking pan.
In a small saucepan over medium heat, melt butter. Once butter is melted, stir in cocoa until smooth. Pour into a mixing bowl.
Then add in sugar and eggs to the mixing bowl and stir together.
Add in vanilla, flour, and salt and beat together well.
Spoon batter into prepared pan.
Bake 25 to 28 minutes, or until cooked through.
Remove pan from oven and top with marshmallows, graham crackers, and candy bar pieces. Place pan back in oven and cook for 2-3 more minutes or until marshmallows start to puff up and chocolate pieces start to melt.
Allow brownies to cool completely, then cut into squares and serve.