Step 1

Preheat the oven to 350 degrees F.

Step 2

Grease a 13x18-inch rimmed baking pan.

Step 3

In a medium bowl, combine the brown sugar and the cinnamon.

Step 4

Add 15 tablespoons of the melted butter to the cinnamon mixture and mix until it is combined. Set aside.

Step 5

In a large bowl, combine 1 cup of the unsalted butter and 1 1/2 cups of the sugar and use an electric mixer to beat on medium speed until it is light and fluffy, about 3-4 minutes.

Step 6

Add the sour cream to the butter mixture and mix until it is well incorporated.

Step 7

Add the milk to the batter mixture and mix well until incorporated.

Step 8

Add the eggs and 3 teaspoons of the vanilla to the batter mixture and mix until it is smooth.

Step 9

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

Step 10

Add the dry ingredients to the wet ingredients and mix until the batter is smooth.

Step 11

Pour the batter into the prepared pan and use a spatula to spread it out evenly.

Step 12

Drizzle the cinnamon sugar mixture on top of the cake, then use a toothpick to swirl it around.

Step 13

Bake the cake until a toothpick inserted in the center comes out with a few crumbs, about 20-25 minutes.

Step 14

Allow the cake to cool in the pan.

Step 15

While the cake is cooling, in a small saucepan over low heat, combine the remaining salted butter, the remaining sugar, the whipped cream, the remaining vanilla extract, and the corn syrup and cook until the sugar has melted.

Step 16

Increase the heat to medium and bring the icing mixture to a boil.

Step 17

Boil the icing mixture, stirring occasionally, for 3 minutes.

Step 18

Transfer the icing mixture from the heat and immediately pour it into a heat-proof glass bowl.

Step 19

Use an electric hand mixer to beat the cream cheese and the powdered sugar into the icing mixture.

Step 20

Allow the icing to cool slightly and thicken.

Step 21

Evenly pour the icing over the cake.

Step 22

Slice and serve warm.