Preheat oven to 350°F (175°C) and grease a 9×13-inch baking pan.
In a large bowl, cream butter, brown sugar, and granulated sugar until smooth.
Add eggs, sour cream, and vanilla extract. Mix until fully combined.
In a separate bowl, whisk flour, cinnamon, baking powder, baking soda, and salt.
Gradually mix dry ingredients into wet ingredients until just combined.
Spread batter evenly into prepared pan and bake 25–30 minutes, until a toothpick comes out clean.
Allow bars to cool completely. Whisk frosting ingredients until smooth and spread over cooled bars.
Slice into bars and serve.