Preheat oven to 350°F. Line standard muffin pan with baking cups. In medium bowl combine flour, baking soda, baking powder and salt. In large bowl, beat butter and sugar with electric mixer until light and fluffy. Add eggs; mix well. Add chocolate and vanilla; beat until well blended. Add dry ingredients in thirds alternating with buttermilk, beating after each addition until smooth. Spoon into baking cups. Bake 18-20 minutes or until toothpick inserted comes out clean. Cool cupcakes in pan on cooling rack for 5-8 minutes. Remove cupcakes from pan; cool completely.