Prep the pan and oven: Heat the oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment, leaving overhang for easy lifting, or grease it well.

Make the crust: In a bowl, combine the yellow cake mix, 1 egg, and 1/2 cup melted butter. Stir until a soft dough forms. It will be thick and a little sticky.

Press into the pan: Use clean hands or a spatula to press the dough evenly into the bottom of the prepared pan. Aim for an even layer so it bakes uniformly.

Beat the cream cheese: In a separate bowl, beat softened cream cheese until smooth and lump-free. This step matters—smooth cream cheese equals a silky top layer.

Make the gooey topping: Add the remaining 3 eggs, the other 1/2 cup melted butter, vanilla, and a pinch of salt to the cream cheese. Beat until combined. Gradually mix in powdered sugar until the batter is thick but pourable and glossy.

Pour and smooth: Pour the cream cheese mixture over the crust and spread it to the edges. Tap the pan lightly on the counter to release air bubbles.

Bake: Bake for 35–45 minutes. You want the edges set and lightly golden, but the center should still jiggle slightly. Do not overbake—the gooey center firms as it cools.

Cool completely: Let the bars cool in the pan on a rack. For the cleanest slices, chill for 1–2 hours before cutting.

Slice and serve: Lift with parchment and cut into squares. Dust with powdered sugar if you like.