Preheat the oven to 350 degrees. Spray a 5×9 loaf pan with cooking spray.
In a large mixing bowl, cream together 6 tablespoons softened butter, ½ cup granulated sugar, and ½ cup brown sugar until light and fluffy.
Add in 2 large eggs, ½ cup milk, ½ cup sour cream, and 2 teaspoons vanilla extract until combined.
In a separate bowl, whisk together 2 cups all purpose flour, 2 teaspoons baking powder, and ½ teaspoon salt. Gradually stir the dry ingredients into the wet ingredients until combined.
In a separate small bowl, mix together ? cup brown sugar, ½ cup granulated sugar, and 1 tablespoon ground cinnamon for the cinnamon swirl.
Pour approximately 1/3 of the batter into the loaf pan. Sprinkle 1/3 of the cinnamon swirl mixture on top. Continue this process until all the batter and cinnamon swirl mixture are used.
Bake for 50-55 minutes until a toothpick inserted into the center of the bread comes out clean.
Let the bread cool for 10-15 minutes on a wire rack. Then carefully remove the bread from the pan and cool completely.
Then the bread is ready to slice, serve and enjoy!
Notes
Store the leftovers in an airtight container or bag at room temperature for up to 3-4 days.