Preheat your oven to 350°F (175°C) and line a sheet pan with parchment paper.

In a large mixing bowl, cream together the granulated sugar and unsalted butter until light and fluffy, about 3-4 minutes.

Mix in the sour cream followed by the milk until well combined.

Add the eggs one by one, mixing well after each addition, then add vanilla extract.

In a separate bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry ingredients into the wet mixture, stirring until just combined.

In another bowl, whisk together brown sugar, cinnamon, and melted butter.

Pour the batter into the prepared sheet pan and spread evenly.

Drizzle the cinnamon filling mixture on top and swirl it lightly with a knife or toothpick.

Bake for 23-25 minutes or until a toothpick inserted into the center comes out clean.

For the icing, combine butter, sugar, heavy cream, and vanilla in a saucepan. Bring to a boil and let thicken for 3-4 minutes.

Remove from heat and stir in cream cheese until fully melted, then gradually add powdered sugar.

Pour the icing over the cooled cake. Cut into squares and serve.