Step 1

Preheat oven to 350 degrees. Lightly grease a 9x13-inch baking pan with cooking spray; set aside.

Step 2

Combine lemon cake mix, butter, and egg in a large bowl; mix until thoroughly combined. (Batter will be thick!) Spread mixture evenly into bottom of baking pan.

Step 3

Whisk together sweetened condensed milk, lemon juice, and lemon zest in a medium bowl. Pour over top of cake mixture. Sprinkle with coconut.

Step 4

Bake 25 to 28 minutes or until set. Cool completely before cutting into squares.