Heat oven to 350°F. Line a 9x13-inch pan with parchment and lightly grease.
Combine cake mix, melted butter, egg, and vanilla. Stir into a thick dough.
Press the dough evenly into the prepared pan to form the crust.
Beat cream cheese until smooth. Add eggs, vanilla, and salt; mix until creamy.
Gradually beat in powdered sugar. Add cream to reach a thick, pourable batter.
Spread the filling over the crust. Do not mix layers.
Bake 32–38 minutes, until edges are golden and center still slightly wobbles.
Cool completely in the pan. Chill 45 minutes for cleaner slices.
Dust with powdered sugar, slice into bars, and serve.