Mix flour, baking soda and salt; set aside. Microwave chocolate and butter in large microwaveable bowl on HIGH 2 min. or until butter is melted. Stir until chocolate is completely melted. Add 1 cup sugar, egg and vanilla; mix well. Stir in flour mixture until well blended. Refrigerate 15 min. or until dough is easy to handle.
Heat oven to 375°F. Shape dough into 1-inch balls; roll in remaining sugar. Place, 2 inches apart, on baking sheets.
Bake 8 to 10 min. or until centers are set. Cool on baking sheets 1 min. Remove to wire racks; cool completely.