Preheat the oven to 350°F (175°C). Gather all your ingredients and equipment.

Prepare your loaf pan by gently oiling it and lining it with parchment paper.

Cream together the softened butter, white sugar, and brown sugar until light and fluffy.

Add the eggs one at a time, mixing well after each, then add milk, sour cream, and vanilla extract.

In a separate bowl, whisk together flour, baking powder, and salt.

Gradually add the dry ingredients to the wet mixture, stirring until just combined.

In a small bowl, mix together cinnamon and granulated sugar for the topping.

Spoon half of the batter into the prepared pan, sprinkle with cinnamon sugar, add remaining batter, and top with more cinnamon sugar.

Bake for 55-60 minutes, checking for doneness with a toothpick.

Cool in the pan for 10-15 minutes, then remove and let cool completely before slicing.