1. Heat oven to 350°F. Grease 8-inch square baking pan.
2. Beat butter, brown sugar, egg and vanilla in medium bowl; beat in flour. Stir in 3/4 cup chocolates and 1/4 cup pecans; spread evenly into prepared pan.
3. Bake 25 to 30 minutes or until lightly browned; remove from oven. Immediately sprinkle remaining 1 cup chocolates over top. Let stand 5 minutes or until chocolate softens. Spread evenly with knife. Immediately sprinkle remaining 1/2 cup pecans over top; press gently. Cool completely in pan on wire rack. Cut into bars. About 16 bars.