1 c. butter
2 c. sugar
1/2 c. unsweetened cocoa powder
4 lg. eggs
2 tsp. vanilla
1 1/2 c. flour
1/4 c. chopped walnuts
1/4 tsp. salt
1/2 c. mini marshmallows

FROSTING:

1/2 c. butter
1/3 c. milk
1/4 c. unsweetened cocoa powder
1/2 tsp. vanilla
About 4 c. powdered sugar

Put butter in large mixing bowl. Microwave on High 1 to 1 1/2 minutes until melted. Stir in sugar and cocoa powder. Add eggs and vanilla, beat vigorously until well blended. Stir in flour, nuts and salt. Let batter rest 10 minutes. Pour into an 11 3/4" x 7 1/2" baking dish. Place on a plastic trivet or an inverted saucer in microwave. Microwave on medium 9 minutes, rotating dish 1/2 turn after 3 minutes. Shield the corners of the dish with small triangles of foil (do not let triangles touch each other or sides of oven). Microwave on High 3 to 5 minutes, rotating dish 1/2 turn once, until top is mostly dry with a few moist spots and pick inserted comes out clean when inserted near center.

Sprinkle marshmallows evenly over top of bars. Let stand about 5 minutes until marshmallows are slightly melted.

FROSTING: Put butter in large bowl. Microwave on High 30 to 60 seconds until melted. Stir in milk, cocoa powder and vanilla. Add sugar and beat until smooth. Spread evenly over marshmallows (bars will be warm). Let stand on flat surface 30 minutes until slightly warm or cool completely and serve at room temperature.