Heat oven to 350°F Grease a 13 x 9 x 2-inch baking pan.
Stir together cocoa and baking soda in large bowl; stir in 1/3 cup butter. Add boiling water; stir until mixture thickens. Stir in sugar, eggs and remaining 1/3 cup butter; stir until smooth. Add flour, vanilla and salt; blend completely. Stir in milk chocolate chips and peanut butter chips. Spread in prepared pan.
Bake 35 to 40 minutes or until brownies begin to pull away from sides of pan. Cool completely in pan on wire rack. Cut into squares.