1. Heat oven to 350 degrees F. Generously coat 13 x 9 x 2-inch baking pan with nonstick cooking spray.
2. Beat together butter, sugar, egg yolk and vanilla in medium-size bowl until well blended. Mix in flour and salt. Press mixture into even layer in bottom of prepared baking pan.
3. Bake in 350 degrees F oven 20 minutes or until top is golden brown. Remove to wire rack. Immediately sprinkle chocolate pieces over top. Let stand 5 minutes to melt. Spread chocolate with metal spatula smoothly over top. Sprinkle with pecans. Cool completely. Cut into bars.