Tip 1: Prep Carefully for Success. Preheat your oven to 350°F (175°C). Lightly grease and flour a 9x13 inch baking pan, or spray with a baking spray that contains flour.
For the Cake Layer: In a large mixing bowl, combine the yellow cake mix, melted unsalted butter, and 2 large eggs. Mix on low speed with an electric mixer until just combined. The mixture will be thick and crumbly. Do not overmix; mixing until just combined ensures a tender bottom layer. Press this mixture evenly into the prepared baking pan to form the bottom crust.
For the Cream Cheese Filling: In a separate medium mixing bowl, beat the softened cream cheese with granulated sugar and 1 teaspoon vanilla extract until smooth and creamy. Ensure your cream cheese is at room temperature for at least 30 minutes to an hour; this prevents lumps and creates a perfectly smooth filling. Beat in the remaining 2 large eggs and a pinch of salt until just incorporated.
Carefully pour the cream cheese filling evenly over the cake layer in the pan.
Bake for 40-45 minutes, or until the edges are lightly golden and the center is mostly set but still slightly jiggly. Tip 3: For that signature gooey texture, do not overbake. The center will firm up as it cools, but should remain moist and rich.
Remove from oven and let cool completely on a wire rack. This can take 1-2 hours. Cooling thoroughly is crucial before glazing.
For the Optional Glaze: Once the cake is completely cool, whisk together the powdered sugar, milk or heavy cream, and 1/2 teaspoon vanilla extract in a small bowl until smooth. Drizzle evenly over the cooled cake.
Cut into squares and serve. Store any leftovers covered in the refrigerator.
Notes
This rich cake is best served chilled or at room temperature. For an extra indulgent treat, serve a slice with a scoop of vanilla bean ice cream or a dollop of fresh whipped cream. Leftovers can be stored in an airtight container in the refrigerator for up to 3-4 days, and often taste even better the next day!