For the bottom cake layer: Preheat the oven to 350 degrees F. Liberally prepare a 9-by-13-inch baking pan with the nonstick method of your choice. Line the pan with parchment paper, then grease the parchment.
In a large bowl, whisk together the yellow cake mix, butter and eggs until combined and thick. Evenly pat the batter into the bottom of the prepared pan.
For the gooey top layer: In the bowl of a stand mixer fitted with the whisk attachment, beat the sugar, cream cheese, vanilla extract, salt and eggs over low speed. Once the sugar is fully incorporated, turn the mixer speed to high. Continue beating until all ingredients are well blended.
Pour the batter into the prepared pan on top of the bottom layer and spread it evenly across the pan using a spatula. Bake for 30 to 35 minutes. The center should still be gooey and will look under-baked.
Let cool on a wire rack for 10 to 15 minutes. Serve in the pan at room temperature.