01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper or grease lightly with butter.
02 - Combine yellow cake mix, melted butter, and egg in a mixing bowl. Stir until a soft, uniform dough forms.
03 - Press the dough evenly across the bottom of the prepared pan using your hands or a spatula.
04 - Beat cream cheese until completely smooth. Add eggs one at a time, beating well after each addition. Mix in powdered sugar, lemon juice, lemon zest, and vanilla extract until fluffy and well combined.
05 - Pour the lemon filling over the base layer and spread evenly. Bake for 35–40 minutes until edges are set but center still jiggles slightly when shaken.
06 - Let cake cool completely in the pan before cutting into squares. Dust with powdered sugar if desired and serve.