Heat oven to 350°F. Grease a 9×13-inch pan and line with a parchment sling.
Make the crust: Stir cake mix, melted butter, and beaten egg until a soft dough forms.
Press dough evenly into the pan. Lightly dock with a fork.
Beat cream cheese in a bowl until smooth and fluffy, about 1 minute.
Add beaten eggs, vanilla, and salt. Mix until creamy and combined.
Gradually beat in powdered sugar until the filling is silky and thick.
Pour filling over the crust and smooth the top.
Bake 32–38 minutes, until edges are set and the center still jiggles slightly.
Cool at least 1 hour in the pan. Dust with powdered sugar, slice, and serve.