Instructions

• Prepare the white cake mix according to package directions and divide the batter between two greased 9-inch round cake pans. Bake as directed on the package and cool the cake layers completely on a wire rack. (You may bake these the night before and wrap them once cool.)
• On assembly day, prepare the brownie mix according to package directions for a 9x13" pan. Line a 9-inch round cake pan with foil and spray the foil with cooking spray.
• Pour brownie batter into the prepared 9-inch round pan, filling no more than 3/4 full. If there is excess batter that will not fit, bake the extra in cupcake liners or a small additional pan (or discard any extra).
• Bake the brownie layer(s) until a toothpick inserted about 1 inch from the side comes out with just a few moist crumbs. For a 9-inch round pan the time may be shorter than a 9x13" pan; check at the lower end of the package time range. Let the brownie layer cool in the pan for 30–45 minutes.
• When the brownie has cooled 30–45 minutes, lift it from the pan using the foil and remove the foil. Place the brownie layer on your cake stand or serving plate and allow it to finish cooling to room temperature.
• While the brownie cools to room temperature, make the chocolate sauce: place 2 ounces chopped semi‑sweet chocolate and 7 ounces sweetened condensed milk in a small heatproof bowl. Microwave in 30‑second increments, stirring between each, until the mixture is smooth. Let the sauce sit 5 minutes to cool slightly.
• Pour the chocolate sauce over the top of the room‑temperature brownie layer on the cake stand. It may spill slightly over the sides. Allow the chocolate to set while you make the frosting.
• Make the frosting: in a stand mixer fitted with the paddle (or using a hand mixer), beat 1/2 cup (1 stick) unsalted butter, 1 (8-ounce) package cream cheese (room temperature), and 1 teaspoon vanilla extract for 1–2 minutes until smooth.
• Add 4 cups powdered sugar to the butter‑cream cheese mixture, 1 cup at a time, beating until the frosting is light and creamy after each addition.
• Add up to 1/4 cup milk, 1 tablespoon at a time, until the frosting reaches a spreadable consistency (use as much milk as needed, up to the full 1/4 cup).
• Once the brownie layer and chocolate topping are at room temperature, place one cooled white cake layer on top of the brownie layer. Spread a thin layer of frosting over that cake layer, then place the second white cake layer on top.
• Apply a thin layer of frosting around the entire cake to create a crumb coat. Chill the cake in the refrigerator until the crumb coat is set, about 15–30 minutes.
• Remove the cake from the refrigerator and use the remaining frosting to finish coating the cake. Use a spatula to create a "c" pattern over the frosted cake for the vintage look.
• Store the finished cake loosely covered in the refrigerator.