Preheat your oven to 350°F (175°C). Grease a loaf pan.
In a mixing bowl, whisk together the flour, sugar, baking powder, and salt.
In another bowl, mix the milk, vanilla extract, egg, and melted butter.
Combine the wet and dry ingredients until just mixed.
In a small bowl, mix the sugar and cinnamon for the swirl.
Pour half of the batter into the loaf pan. Sprinkle half of the cinnamon sugar mixture over the batter. Pour the remaining batter on top and sprinkle the rest of the cinnamon sugar mixture.
Use a knife to swirl the cinnamon sugar into the batter.
Bake for 40 minutes or until a toothpick inserted into the center comes out clean.
Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.