Step 1: Preheat and Prepare the Pan

• Preheat your oven to 350°F (175°C).

• Grease and line a 9×13-inch baking dish with parchment paper.

Step 2: Create the Cake Batter

• In a large mixing bowl, combine yellow cake mix, melted butter, milk, and eggs.

• Mix until smooth, then spread half of the batter into the bottom of the prepared pan.

Step 3: Make the Cinnamon Swirl

• In a small bowl, stir together brown sugar, ground cinnamon, and melted butter.

• Drizzle half the cinnamon mixture evenly over the cake batter.

Step 4: Prepare the Cream Cheese Layer

• Beat together softened cream cheese, powdered sugar, melted butter, and vanilla extract until smooth.

• Spread this creamy filling gently over the cinnamon swirl layer.

Step 5: Assemble the Cake

• Pour the remaining cake batter over the filling.

• Drizzle the rest of the cinnamon swirl mixture on top.

• Use a knife or skewer to swirl everything together slightly for a marbled finish.

Step 6: Bake the Cake

• Bake for 40–45 minutes, or until the edges are firm but the center is still a little gooey.

• Allow the cake to cool completely in the pan before frosting.

Step 7: Make the Sticky Toffee Buttercream

• In a saucepan, melt butter and brown sugar over medium heat until bubbly and caramelized.

• Remove from heat, stir in heavy cream and vanilla, and let cool for 5 minutes.

• Beat in powdered sugar, adding more as needed to reach a spreadable consistency.

Step 8: Flood the Cake

• Generously spread the sticky toffee buttercream over the cooled cake.

• Use a spoon to swirl and flood the frosting into the edges and ridges of the cake for a gorgeous, glossy finish.