Grandma's Melt in your mouth Brownies

It is not a family party without these delightfully delicious Brownies made by Grandma Janice. Today is the first time I have made them. These are indeed dangerous!

1 Cup Butter
1/3 Cup Cocoa
2 Cups Sugar
4 Eggs well beaten
1 1/2 Cups Flour
1 1/2 Cups Coarsely Chopped Walnuts
2 teaspoons Vanilla

*Pour batter into greased cookie sheet (15 1/2 x 10 1/2 x 1 Inch) and spread evenly. Bake @ 350 degrees for 25 minutes. Remove from oven and put 1 pound miniature marshmallows over the top. Be sure they are in a single layer close to the edge. Return to oven for about 3 minutes or until light golden brown. Remove from oven and cool for about 1 hour. Top with Icing.

Icing:
1/2 Cup Butter
2 Cups Powdered Sugar
1/4-1/3 Cup Cocoa
1/3 Cup Evaporated Milk
1 Teaspoon Vanilla
Combine ingredients and spread over brownie marshmallow bars.