1. Heat oven to 350°F. Line 13x9x2-inch baking pan with foil; grease foil.
2. Stir together cocoa and baking soda in large bowl; stir in 1/3 cup melted butter. Add boiling water; stir until mixture thickens. Stir in sugar, eggs, vanilla and remaining 1/3 cup butter; stir until smooth. Add flour; stir until blended. Stir in peanut butter chips. Pour into prepared pan.
3. Bake 35 to 40 minutes or until brownies begin to pull away from sides of foil. Cool completely in pan. Cover; refrigerate until firm. Remove from pan; remove foil. Cut into shapes with cookie cutters, or cut into squares. Just before serving, sprinkle with powdered sugar, if desired. About 12 large brownies or 36 squares.