1 box yellow cake mix, 4 large eggs, 3/4 cup veg oil, 1 cup sour cream, 1 cup brown sugar, 1 tbs cinnamon, 2 cups powdered sugar, 1/4 cup milk, 2 teaspoons vanilla extract
Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch baking dish. In a large bowl, combine the cake mix, eggs, oil, and sour cream. Beat until smooth.
Pour half of the batter into the prepared baking dish. In a small bowl, combine the brown sugar and cinnamon. Sprinkle over the top of the batter in the baking dish.
Pour the remaining batter over the brown sugar mixture. Using a knife, swirl the batter to create a marble effect.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool completely before frosting.
In a medium bowl, whisk together the powdered sugar, milk, and vanilla extract until smooth and runny.
Pour the frosting over the cooled cake and spread it into an even layer. Let the frosting set before serving.
For a richer flavor, use whole milk instead of 2% milk in the cake batter and frosting. If you want a sweeter cake, add more brown sugar or powdered sugar.
You can also add other flavors to the cake batter or frosting, such as nutmeg, allspice, or maple extract.
To make a honey bun cake with a pecan streusel topping, combine 1/2 cup chopped pecans, 1/4 cup brown sugar, and 1 tablespoon cinnamon in a small bowl.