CRUST: Preheat oven to 350°F. Spray 8x8-inch square pan with cooking spray. Stir cookie mix and melted butter together in medium bowl. Mixture will be crumbly. Press cookie dough on bottom of pan. Bake 12 to 14 minutes, until lightly browned.
LEMON FILLING: Whisk sugar, flour, eggs, and lemon juice together in a clean bowl. Pour filling over hot cookie crust.
Bake 20 to 24 minutes, until center is set, and edges are just starting to brown.
Cool at room temperature for 30 minutes. Refrigerate uncovered until cold, at least 2 hours. Dust with confectioners’ sugar. Cut into bars and serve!
