**Preheat the oven** Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish or line it with parchment paper.

**Form the base** In a mixing bowl, combine the cake mix, melted butter, and 1 egg. Stir until a soft dough forms. Press the dough evenly into the prepared baking dish.

**Prepare the lemon layer** In a separate bowl, beat the softened cream cheese until smooth. Add the remaining 2 eggs, powdered sugar, lemon juice, and lemon zest (if using). Beat on medium speed until well combined and slightly fluffy.

**Assemble** Pour the lemon cream cheese mixture over the base layer, spreading it evenly.

**Bake** Place the baking dish in the preheated oven and bake for 25–30 minutes, or until the edges are set and lightly golden. The center may still look slightly soft but will set as it cools. Avoid overbaking to keep the top layer gooey.

**Cool and serve** Let the bars cool completely in the pan. Dust with additional powdered sugar if desired. Slice into squares and serve.