Heat oven to 350 degrees. Grease 13 x 9 baking pan. Stir together cocoa and baking soda in large bowl; stir in 1/3 c. butter. Add boiling water; stir until mixture thickens.
Stir in sugar, eggs and remaining 1/3 c. butter; stir until smooth. Add flours, vanilla and salt; stir until blended. (Optional: stir in chocolate chips.) Pour into prepared pan.
Bake 30-35 minutes, or until brownies begin to pull away from sides of pan. Cool completely.
Frost brownies (optional)