01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper or lightly grease the surface.
02 - Combine the cake mix, melted butter, and egg in a mixing bowl. Mix until a soft, uniform dough forms.
03 - Press the dough evenly across the bottom of the prepared baking pan to create the base layer.
04 - Beat the cream cheese until smooth. Add eggs one at a time, mixing well after each addition. Blend in powdered sugar, lemon juice, lemon zest, and vanilla extract until the mixture is fluffy and smooth.
05 - Pour the lemon filling mixture over the prepared base and spread evenly. Bake for 35-40 minutes until edges are set and the center retains a slight jiggle. Avoid overbaking to maintain the gooey texture.
06 - Let the cake cool completely before cutting into squares. Optionally dust with additional powdered sugar before serving.