¼ cup chopped nuts
2 cups small marshmallows

Cream butter and sugar at medium speed with an electric mixer until creamy.  Add eggs, one at a time beating well after each addition.  Add flour, salt and cocoa.  Beat until blended.  Stir in vanilla followed by the chocolate chips.

Pour batter into a parchment lined 13 x 9 inch pan.  Sprinkle chopped nuts on top.  Bake at 350° for 40 minutes.  Remove from oven, sprinkle 2 cups of small marshmallows evenly over the top. Return to the oven for 2 minutes.  Spread frosting over warm fudge bars.  Cool, then chill before serving.  

Frosting

½ cup softened butter
3 cups powdered sugar
¼ cup unsweetened cocoa
1/8 tsp salt
1 tsp vanilla
¼ cup milk

Cream butter.  Add powdered sugar, cocoa, salt, vanilla and milk.  Beat with an electric mixer until smooth.