In a large bowl or mixer, beat together cake ingredients (cake mix, 1 egg and butter) until just combined, then transfer mixture to a 9×13-inch baking dish.
In a separate bowl, beat cream cheese until smooth and creamy, then mix in eggs one at a time and add vanilla extract.
Once smooth, and working in batches, if necessary, mix in powdered sugar.
Pour filling over cake batter, then place baking dish in oven.
Bake for 50-60 minutes, or until edges are lightly browned and have pulled away from the sides of the pan. Center should still be a little jiggly.
Remove from oven and let cool 10-15 minutes, or until set. Enjoy!