1. Prepare the Base:

– Preheat oven to 350°F (175°C) and grease a 9×13-inch baking dish.

– In a bowl, combine the cake mix, egg, and melted butter. Mix until well combined. Press the mixture evenly into the bottom of the prepared dish.

2. Make the Lava-Flow Filling:

– In a large mixing bowl, beat the cream cheese until smooth.

– Add eggs and vanilla extract, mixing well.

– Gradually mix in the powdered sugar until fully incorporated. Stir in melted butter until smooth.

– Pour the filling mixture over the base.

3. Create the Cinnamon Swirl:

– In a small bowl, mix ground cinnamon and brown sugar. Sprinkle this mixture evenly over the cream cheese filling.

– Use a knife to gently swirl the cinnamon mixture into the filling, creating a marbled effect.

4. Bake:

– Bake in the preheated oven for 40-45 minutes, or until the edges are set but the center remains gooey. Avoid overbaking for a soft, lava-like center.

5. Add the Glaze:

– In a small bowl, whisk together powdered sugar, milk, and vanilla until smooth. Drizzle over the warm cake if desired.

6. Cool and Serve:

– Allow the cake to cool for at least 30 minutes before slicing. Serve warm or at room temperature for the ultimate gooey experience.