Heat oven to 350°F. Grease a 9×13-inch pan or line with parchment.
Stir cake mix, melted butter, and 1 egg in a bowl until a soft dough forms.
Press the dough evenly into the prepared pan to make the crust.
Beat cream cheese until smooth. Add remaining 2 eggs, vanilla, and salt; mix until silky.
Gradually beat in powdered sugar until glossy and thick, scraping the bowl as needed.
Pour filling over the crust and spread to the edges.
Bake 32–38 minutes until edges are set and the center still jiggles slightly.
Cool in pan until lukewarm, then dust with powdered sugar. Slice into squares to serve.