Preheat your oven to 350°F (175°C) and grease a 9x5-inch loaf pan with butter or cooking spray.

In a large mixing bowl, whisk together the flour, baking powder, salt, and ground cinnamon.

In another bowl, beat the softened butter and sugar together until light and fluffy.

Add the eggs one at a time, then mix in the milk and vanilla extract until smooth.

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

Pour half of the batter into the prepared pan, sprinkle with half of the cinnamon sugar mixture, then add the remaining batter and top with the remaining cinnamon sugar.

Using a knife, gently swirl the batter, then bake for 50-60 minutes or until a toothpick comes out clean.

Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.