01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper or lightly grease with butter.
02 - Combine the cake mix, melted butter, and egg in a mixing bowl. Mix until a soft, thick dough forms.
03 - Press the dough evenly into the bottom of the prepared pan using your hands or the back of a spoon to create a uniform base layer.
04 - Beat the softened cream cheese in a separate bowl 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 completely smooth.
05 - Pour the lemon cream cheese mixture over the base layer and spread evenly. Bake for 35-40 minutes until the edges are set and golden but the center still has a slight jiggle.
06 - Let the cake cool completely in the pan before cutting into squares. Optionally dust with additional powdered sugar before serving.