Reserve 1 tablespoon flour in small bowl. In medium bowl, mix remaining flour, cocoa, baking soda, baking powder and salt; set aside. In large bowl, beat softened butter and sugar with electric mixer on high speed until light and fluffy. Beat in eggs, one at a time, scraping bowl occasionally. Beat in vanilla. Add flour mixture to sugar mixture alternately with buttermilk on low speed, beating after each addition, until smooth. Add 1 cup semisweet chocolate chips to reserved flour; stir to coat chips in flour. Stir chips and flour into batter. Pour into pan.