Preheat your oven to 350°F (175°C) and grease your loaf pan.

In a medium-sized bowl, whisk together all-purpose flour, baking powder, and salt.

In a large mixing bowl, cream together the softened unsalted butter and granulated sugar until light and fluffy.

Add the egg, milk, vanilla extract, and vegetable oil into the mixture, blending until fully combined.

Gradually mix the dry ingredient mixture into the wet ingredients, being careful not to overmix.

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

Pour half of the batter into the greased loaf pan, sprinkle with half of the cinnamon sugar mixture, add the remaining batter, and top with the rest of the cinnamon sugar.

Bake for 45 minutes or until a toothpick inserted comes out clean.

Remove from the oven and cool in the pan for 10 minutes before transferring to a wire rack.