Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish.

In a large bowl, combine cake mix, milk, oil, eggs, and vanilla extract. Beat until smooth, about 2 minutes.

Pour the batter into the prepared pan and bake for 25–30 minutes or until a toothpick comes out clean.

While the cake bakes, mix the brown sugar, cinnamon, and melted butter in a small bowl to make the cinnamon filling.

When the cake is done, let it cool for 5–10 minutes. Then use the handle of a wooden spoon to poke holes all over the cake, spacing them about 1 inch apart.

Pour the cinnamon filling evenly over the cake, letting it soak into the holes.

In another bowl, whisk together sweetened condensed milk, powdered sugar, milk, and vanilla (and cream cheese, if using).

Pour the glaze over the cake, spreading it out to cover the top.

Let the cake cool completely, then refrigerate for at least 1 hour before serving for best flavor and texture.

Slice, serve, and enjoy!