Preheat oven to 350°F (175°C). Grease a loaf pan or line with parchment paper.
In a bowl, whisk flour, baking powder, and salt. Set aside.
In another bowl, beat sugar, egg, milk, melted butter, and vanilla until smooth.
Gradually fold dry ingredients into wet until just combined (don’t overmix).
Mix brown sugar and cinnamon in a small bowl.
Pour half the batter into the loaf pan. Sprinkle half the cinnamon-sugar mix.
Add remaining batter, then top with the rest of the cinnamon-sugar.
Drizzle 1 tbsp melted butter over the top.
Bake 50–55 mins or until a toothpick comes out clean.
Cool in the pan for 10 mins, then transfer to a wire rack.
