• Preheat oven to 180 degrees.
• Grease a 9 inch square pan with butter, sprinkle with flour and discard the excess flour.
• Beat butter and sugar in a bowl until fluffy.
• Add eggs and vanilla, and continue beating until well combined.
• Mix flour with salt, cocoa, semi-sweet chocolate chips and walnut in a bowl.
• Fold in flour mixture with egg mixture gently.
• Pour batter into prepared pan, spread evenly.
• Bake for about 20 minutes, allow to cool.

  Top Layer

• Place butter, milk, sugar and cocoa in a pan over low heat.
• Stir to combine.
• Add vanilla and marshmallows while stirring until it melts.
• Pour over brownies, spread evenly, allow to cool.
• Arrange miniature marshmallows on top the chocolate layer.
• Turn on oven broiler, place the brownies on the center rack, and lightly toast the marshmallows.
• Remove brownies from the oven and cool in the pan before cutting.