Cream butter and sugar in large bowl. Add eggs and vanilla, beat until mixed well with butter and sugar mixture. Add all dry ingredients, just until incorporated. Fold in nuts.
Pour into foil lined, greased 8 inch square pan.
Bake in 350 degree oven for about 25 minutes until knife inserted in center comes out with a few moist crumbs attached.
Frosting: Melt chocolate and butter over low heat. Combine chocolate mixture with remaining ingredients, beat until thoroughly blended. Frost cooled brownies, cut when cooled completely. Yields about 2-3 dozen bite sized pieces.