Preheat the oven to 350 degrees F. Spray a 9x13-inch baking dish with nonstick cooking spray.
In a large mixing bowl, combine 1 box yellow cake mix, 1 large egg, and ½ cup melted butter.
Mix with a hand mixer or stand mixer until well combined.
Spread the cake batter evenly into the prepared baking dish.
In a separate mixing bowl, beat 1 package (8 ounces) cream cheese until smooth and creamy.
Add 2 large eggs, ½ cup melted butter, and 1 teaspoon vanilla extract. Mix until well combined.
Gradually add 4 cups powdered sugar, about 1 cup at a time, mixing after each addition until the filling is smooth.
Carefully spread the cream cheese filling evenly over the cake batter.
Bake for 40 to 50 minutes, until the edges are lightly browned and the center is still slightly gooey. Be careful not to overbake, as the center will continue to set as the cake cools.
Allow the cake to cool completely at room temperature before cutting into 12 squares.
Serve and enjoy!
Notes
Make sure that all the ingredients are at room temperature to ensure that they mix well before making this cake recipe. Refrigerate any leftovers in an airtight container for up to 1 week.