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

In a large bowl, whisk together the flour, baking powder, salt, and 1 teaspoon of cinnamon. Set aside.

In another bowl, cream together the softened butter and 1 cup of sugar until light and fluffy.

Add the eggs one at a time, mixing well after each addition. Then stir in the milk and vanilla extract until combined.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.

Pour half of the batter into the prepared loaf pan. In a small bowl, mix together 1/2 cup of sugar and 1 tablespoon of cinnamon. Sprinkle half of this mixture over the batter in the pan.

Pour the remaining batter into the pan and top with the remaining cinnamon sugar mixture.

Use a knife to swirl the batter gently, creating a marbled effect.

Bake in the preheated oven for 50-60 minutes, or until a toothpick inserted into the center comes out clean.

Allow the bread to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.