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

In a large mixing bowl, cream together 1/2 cup softened butter, 1 cup brown sugar, and 1/2 cup granulated sugar until smooth and fluffy.

Add 2 room temperature eggs, 1/2 cup sour cream, and 2 teaspoons vanilla extract and mix until well combined.

In a separate bowl, whisk together 2 cups all-purpose flour, 1 teaspoon baking powder, 1/2 teaspoon baking soda, 1 tablespoon ground cinnamon, and 1/2 teaspoon salt.

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

Pour and spread the batter evenly into your prepared baking pan.

Mix together 1 tablespoon of ground cinnamon with 1 tablespoon of sugar and sprinkle over the batter.

Bake for 25-30 minutes; check for doneness with a toothpick.

Allow the bars to cool in the pan on a wire rack.

Prepare the frosting by beating together 1 cup powdered sugar, 2 tablespoons milk, and 1 teaspoon vanilla extract until smooth.

Once the bars are cool, spread the frosting over them and cut into squares.