Prepare the Apple Swirl: In a bowl, toss diced apples with brown sugar and cinnamon. Set aside so the flavors soften and mingle.
Cream the Batter: Beat butter and sugar until pale and fluffy. Add eggs one at a time, then vanilla, mixing gently until smooth.
Build the Dough: Whisk flour and baking powder together. Add to the batter alternately with milk, stirring just until combined. The batter should be thick and soft.
Layer the Loaf: Pour half the batter into a greased loaf pan. Spoon half the apple mixture over the top. Add remaining batter, then finish with the rest of the apples.
Create the Cinnamon Swirl: Use a knife to gently swirl through the layers, creating soft ribbons without overmixing.
Bake Until Golden: Bake at 350°F (175°C) for 50–60 minutes, until a toothpick comes out mostly clean and the top is golden and fragrant.
Glaze with Care: Let the loaf cool slightly. Whisk glaze ingredients and drizzle slowly over the warm bread so it settles into the crumb.
