Preheat oven to 350°F. Line a 13" x 9" metal baking pan with parchment paper then spray evenly with nonstick cooking spray. In a large bowl, combine cake mix, melted butter and 1 egg, stirring until a stiff dough forms. Press mixture evenly onto bottom of prepared pan to create a thin crust. Bake 20 minutes or until light brown. Remove crust from oven and allow to cool slightly. In a separate bowl, whisk together remaining 2 eggs, corn syrup, sugar, egg white and vanilla until smooth. Stir in chopped pecans and pecan halves then pour pecan mixture over prepared crust. Bake 25–28 minutes or until filling is set. Remove from oven and cool on a wire rack. Cut into 48 squares and serve.