Heat the oven to 350°F. Grease a 9 x 13-inch baking pan, then line it with parchment paper if you want especially easy removal, leaving some overhang along the sides.

Stir the dry lemon cake mix, melted butter or margarine, and one large egg together until a thick dough forms. Press the dough evenly over the bottom of the prepared pan.

Beat the softened cream cheese, powdered sugar, one large egg, and fresh lemon juice until smooth. Stir in the lemon zest if using.

Spread the lemon-cheese mixture evenly over the crust. Bake for approximately 25–30 minutes, until the edges are lightly golden and the topping is set with a slight jiggle in the center.

Cool the bars completely in the pan before cutting. For the cleanest slices, chill the cooled bars for 1–2 hours, then dust with powdered sugar if desired.