Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 15x10-inch sheet pan.

Make the cake mix layer: Stir cake mix, melted butter, and egg in a bowl until well combined. Press mixture into the prepared sheet pan.

Make the cream cheese layer: Beat cream cheese and eggs in a bowl until combined. Gradually mix in confectioners' sugar. Pour mixture over the cake mix layer in the sheet pan.

Bake in the preheated oven for 15 minutes. Reduce the oven temperature to 300 degrees F (150 degrees C), and continue to bake until a toothpick inserted at the center of the pan comes out with just a few moist crumbs clinging to it, 30 to 35 minutes more.

Remove from the oven and let cool completely before cutting into 24 bars.