Mix flour, baking soda and salt until well blended; set aside. Beat butter and sugars in large bowl with electric mixer until light and fluffy.
Add egg and vanilla; beat until well blended. Gradually add flour mixture, mixing well after each addition. Stir in chopped chocolate.
Drop rounded tablespoonfuls of dough, 2 inches apart, onto baking sheets.
Bake 12 to 13 min. or until lightly browned. Cool on baking sheets 1 min.
Remove to wire racks; cool completely.
Serve immediately. (Or, wrap cooled cookies in plastic wrap and place in tightly covered container or resealable plastic bag. Freeze up to 1 month. Thaw at room temperature before serving.)