Preheat oven to 350F degrees. Spray a 9x13 baking pan with nonstick cooking spray. Set aside.
In a medium bowl, whisk together flour, baking powder, and salt. Set aside
In a large bowl using an electric mixer, beat together butter, ¾ cup of granulated sugar, and brown sugar on medium speed; mix until smooth. Beat in egg, egg yolk, lemon zest, and lemon juice; just until combined.
Add flour mixture; mix just until combined.
Spread dough evenly into prepared pan. Evenly sprinkle remaining ¼ cup of granulated sugar onto the top of the spread dough.
Bake for 23-27 minutes or until edges are lightly browned. Use a toothpick to check for doneness. Cool completely on wire rack. Cut into bars. Eat & Enjoy!
Lemon Sugar Cookie Bars should be stored in an airtight container; will keep 3+ days.