Preheat your oven and prepare your loaf pan by greasing it or lining it with parchment paper.

In a mixing bowl, combine the sifted all-purpose flour, baking powder, and salt. Stir with a whisk.

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

Add the eggs, one at a time, mixing well after each addition.

Pour in the vanilla extract and room-temperature milk, stirring until well combined.

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

Mix the light brown sugar with ground cinnamon in another bowl.

Pour half of the batter into the prepared loaf pan, add half of the cinnamon-sugar mixture on top, and swirl gently.

Repeat with the remaining batter and cinnamon-sugar mixture, swirling lightly.

Drizzle the melted butter over the top of the batter.

Place the loaf pan in the preheated oven and check for doneness.

Once baked, let it cool in the pan for a few minutes before transferring it to a wire rack.

While the loaf cools, whisk together the powdered sugar and milk or water for the glaze.

Once the loaf has cooled, drizzle the glaze on top.