Start by preheating your oven to 350°F (175°C). This ensures it’s hot and ready for the bars as soon as you’re done preparing the batter.

Grease a 9x13-inch baking pan with non-stick spray or a little butter. For easy removal later, you can also line the pan with parchment paper. This step is crucial to avoid any sticking and to keep the bars looking perfect!

In a large mixing bowl, whisk together the lemon cake mix, eggs, and vegetable oil. Stir the ingredients together until the batter is smooth and well combined. It will be thicker than a traditional cake batter, but that's exactly what we want for the base.

Pour the batter into your prepared baking pan. Use a spatula to spread it evenly, making sure it covers the entire bottom of the pan. This will create the base layer for your lemon bars.

Place the pan in the oven and bake for 15-20 minutes, or until the edges begin to turn golden and a toothpick inserted into the center comes out clean. The base should be firm yet slightly soft to the touch. Remove it from the oven and set aside to cool for a few minutes.

While the base is cooling, take a small bowl and whisk together the lemon juice, lemon zest (if using), and powdered sugar. This mixture will form the zesty topping for your bars.

Once the base has cooled slightly, pour the lemon filling over the cake layer. Use a spatula to spread it evenly, ensuring every bite gets a bit of that tangy goodness.

Return the pan to the oven and bake for an additional 10-15 minutes, or until the filling is set and slightly golden on top. It should no longer jiggle when you shake the pan gently.

After baking, let the lemon bars cool completely in the pan. Once they’ve cooled down, dust the top with powdered sugar for that sweet finishing touch. This adds just the right amount of sweetness to balance the tangy lemon flavor.

Once completely cooled, slice the lemon bars into squares. You can cut them into large or small pieces, depending on how you prefer to serve them!