Preheat the oven to 350°F (175°C). Grease and flour a 9×13 inch baking pan.
In a large mixing bowl, combine the lemon cake mix and lemon-flavored Jello powder.
Add the water, vegetable oil, eggs, and sour cream to the dry ingredients.
Using an electric mixer, beat the mixture on medium speed for 2 minutes until smooth and well combined.
Pour the batter evenly into the prepared baking pan.
Bake in the preheated oven for 30 minutes or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and allow it to cool completely in the pan on a wire rack.
In a small bowl, whisk together the powdered sugar, fresh lemon juice, and lemon zest until smooth to make the glaze.
Once the cake is fully cooled, spread the lemon glaze evenly over the top.
Cut into 12 squares and serve.