Heat oven to 350°F. Generously coat 13 x 9 x 2-inch baking pan with nonstick cooking spray.
Beat together butter, sugar, egg yolk and vanilla in medium-size bowl until well blended. Mix in flour, salt and the 1/3 cup finely chopped hazelnuts. Press into even layer on bottom of prepared pan.
Bake at 350°F for 20 minutes or until top is golden brown. Remove pan to wire rack and cool 10 minutes. Spread top evenly with chocolate-hazelnut spread. Sprinkle with remaining hazelnuts. Chill to set top. Cut into 24 bars.