Preheat your oven to 350°F (175°C) and grease and flour a 9x13-inch baking pan.

In a large mixing bowl, combine the all-purpose flour, granulated sugar, vegetable oil, eggs, sour cream, and vanilla extract. Add the baking powder, baking soda, and salt. Mix until smooth.

In a separate bowl, mix the brown sugar and ground cinnamon together.

Pour half of the cake batter into the prepared baking pan. Sprinkle half of the cinnamon-brown sugar mixture over the batter. Pour the remaining batter on top and sprinkle the rest of the cinnamon-brown sugar mixture. Use a knife to swirl the layers together gently.

Bake for 40-45 minutes. Check for doneness with a toothpick.

While the cake is baking, whisk together the powdered sugar and milk until smooth to prepare the glaze.

Once the cake has cooled for about 15 minutes, drizzle the glaze over the cake.