Step 1: Prepare the Base: Preheat oven to 350F (175C). Grease and flour a 9x13 inch baking pan to prevent sticking. This will ensure the cake releases easily after baking.
Step 2: Combine Base Ingredients: In a large bowl, combine the yellow cake mix, softened cream cheese, melted butter, 1 egg, and vanilla extract. Mix until well combined. The mixture will be thick. This forms the foundation of the cake, so ensuring a smooth and even batter is important.
Step 3: Prepare the Base in Pan: Press the mixture into the prepared baking pan evenly. It might be easier to use your hands to press it into an even layer. Because the mixture is thick, even distribution is vital for uniform baking.
Step 4: Make the Topping: In a separate bowl, beat the remaining 2 eggs and powdered sugar until smooth and creamy. This topping is the key element of flavor.
Step 5: Pour Topping Over Base: Pour the powdered sugar mixture evenly over the cake base. Spread it gently to ensure it covers the entire surface. This distribution ensures the finished product has uniform flavor.
Step 6: Dot with Butter: Dot the top of the cake with the 1/4 cup of butter pieces. This ensures the topping maintains its consistency.
Step 7: Bake: Bake in the preheated oven for 30-35 minutes, or until the edges are golden brown and the center is slightly gooey. The cake is ready when a toothpick inserted near the edge comes out clean, but the center remains soft.
Step 8: Cool and Serve: Let the cake cool completely before cutting into squares. Dust with additional powdered sugar, if desired. Cooling allows the cake to set, making it easier to cut and serve.
Optional: For a richer flavor, use brown butter in the base. Simply melt the butter in a saucepan over medium heat, stirring constantly until it turns golden brown and has a nutty aroma. Allow it to cool slightly before adding to the cake mix. A sprinkle of sea salt on top can also enhance the sweetness.