Mix cake mix, 1 egg and butter until smooth. Press into prepared pan.
FILLING
Add the cream cheese, 2 eggs, vanilla powdered sugar and lemon zest to a bowl and mix with an electric mixer until smooth.
Spread filling evenly over the crust.
Bake at 350 for 40-45 minutes or until edges are golden brown and a toothpick inserted into the center comes out clean.
Cool completely and top with powdered sugar if desired.
Notes
Use Room Temperature Eggs
This helps the filling blend smoothly and bake evenly. Cold eggs can cause the mixture to curdle slightly or bake unevenly.
Zest It Up Add a teaspoon of fresh lemon zest to the filling for a more vibrant citrus flavor. It gives the bars a homemade touch that balances the sweetness of the cake mix.
Don’t Overbake The bars should have a slight jiggle in the center when you pull them from the oven. They’ll firm up as they cool. Overbaking can lead to a dry, rubbery texture.
Cool Completely Before Cutting Let the bars cool at room temperature, then chill them in the fridge for cleaner slices. A warm filling tends to stick to the knife and crumble.
Line Your Pan with Parchment This makes it easier to lift the bars out for slicing and prevents sticking. Leave a little overhang for easy removal.
Dust with Powdered Sugar Just Before Serving If you dust too early, the sugar can dissolve into the surface. For a pretty finish, wait until the bars are fully cooled.
Make Them Ahead These bars actually taste better the next day as the flavors meld. Store them in an airtight container in the fridge for up to 5 days.