Preheat oven to 350~F. Grease 13x9" pan. In medium bowl, combine cocoa and baking soda; blend in 1/3 c melted butter. Add the boiling water; stir until mixture thickens. Stir in sugar, eggs and remaining 1/3 c melted butter; stir until smooth. Add flour, vanilla and salt; blend completely. Stir in chocolate chips; pour into prepared pan. Bake 35-40 minutes or until brownies begin to pull away from sides of pan. Cool completely; frost with Buttercream frosting. Cut into squares.

Buttercream Frosting: Cream butter in small mixing bowl; add cocoa and sugar alternately with milk. Beat to spreading consistency; blend in vanilla.