Preheat the oven to 350°F (175°C). Line a 9×9 inch baking pan with parchment paper or lightly grease it.
In a large bowl, combine the lemon cake mix, melted butter, eggs, sour cream, lemon zest, and vanilla extract. Mix until all ingredients are well incorporated and the batter is smooth.
Pour the batter into the prepared baking pan and spread it evenly with a spatula.
Bake for 22 to 25 minutes, or until a toothpick inserted into the center comes out clean.
Remove the pan from the oven and allow the bars to cool completely in the pan on a wire rack.
In a small bowl, whisk together the powdered sugar and fresh lemon juice until smooth to create the glaze.
Once the bars are completely cooled, drizzle the lemon glaze evenly over the top.
Allow the glaze to set for about 10 minutes before cutting into 16 bars and serving.