Method
In a large mixing bowl, blend butter, sugar and vanilla. Add eggs; beat well with a spoon. In a small bowl, combine flour, cocoa, baking powder, and salt; gradually blend into wet mixture. Stir in pecans. Spread batter in lightly greased and floured 8 or 9 inch square pan. Bake at 350 degrees for 20 to 25 mins, or until brownies just begin to pull away from the sides of the pan. Prepare icing and frost while brownies are still warm.

Icing
Place powdered sugar in medium mixing bowl. Melt 3 tbsp of butter or margarine in a small saucepan over low heat; stir in 2 tbsp of cocoa, blending until smooth. Add milk; stir constantly over low heat until mixture has thickened slightly. Pour hot mixture over the powdered sugar; beat until smooth. Stir in ¼ tsp vanilla and ¼ tsp chopped walnuts. Spread warm icing over still–warm brownies.