Heat oven to 350°F. Grease or line cookie sheets with cooking parchment paper. In medium bowl, stir together flour, cocoa, baking soda and salt; set aside. In large bowl, beat 1 cup sugar, the eggs and vanilla with electric mixer on medium speed 2 minutes or until well blended. Add cooled chocolate mixture; beat on low speed until combined. Slowly beat in flour mixture until soft dough forms. Stir in toffee bits.