In a mixing bowl, combine cocoa and baking soda; blend in 1/3 cup melted butter. Add boiling water, stirring until thickened. Stir in sugar, eggs, vanilla and remaining butter. Add flour, cinnamon and salt. Fold in chocolate chips. Pour into a greased 13" x 9" x 2" baking pan. Bake at 350 degrees for 40 minutes or until brownies test done. Cool. For frosting, cream butter in a mixing bowl. Combine cocoa, sugar and cinnamon; add alternately with the milk. Beat to a spreading consistency; add vanilla. Add more milk if necessary. Spread over the brownies.