I've used this quick MW recipe for years and love 'em!
1/2 cup butter or margarine
1 cup sugar. 3/4 cup flour
2 eggs. 2 tsps vanilla
1/3 cup cocoa. 1/2 cup walnuts if desired
Place butter in 8" x 8" MW able baking dish. MW on high for 1 minute or till melted.
Carefully pour butter into batter bowl and set baking dish aside.
Add sugar, eggs and cocoa to melted butter and mix with a wooden spoon.
Pour batter into baking dish and cover with a paper towel.
MW on high for 5 to 7 minutes (I do 5) or till toothpick tests clean.
I usually will sprinkle choc chips and/or peanut butter chips across the top of the batter (whether boxed mix or this MW mix) before baking. Our grown grandsons have always loved them that way!