http://www.youtube.com/watch?v=uNx6dekPgNQ

10 T unsalted butter
1 1/3 C sugar
2/3 C unsweetened cocoa (prefer Dutch processed)
1 t vanilla
2 eggs
1/2 C flour
1/2 t baking powder
1/4 t salt
1/4 C sour cream

Line the bottom and sides of an 8" pan with aluminum foil for easy removal
and grease the foil

Mix the sugar and cocoa together and get rid of any lumps
Melt the butter and add it to the sugar cocoa
Mix together
Add in the vanilla and eggs, one at a time until the batter is smooth and
shiny
In a separate bowl, mix together the flour, salt, and baking powder
Fold the dry into the wet and finally fold in the sour cream

Pour into an 8" greased pan and bake at 325 for 28-30 minutes until a 
toothpick comes out with moist crumbs sticking to it.