Preheat your oven to 350°F (175°C). Grease and flour a 9×5-inch loaf pan.
Mix brown sugar and cinnamon together in a small bowl; set aside.
In a large bowl, beat white sugar and butter until light and fluffy.
Beat in eggs one at a time, then stir in vanilla extract.
In a separate bowl, whisk together flour and baking powder. Add to the butter mixture alternately with milk, stirring until smooth.
Pour half of the batter into the prepared pan. Top with half of the apples and half of the cinnamon sugar mixture. Repeat with remaining batter and toppings.
Bake for 30–40 minutes, or until a toothpick inserted in the center comes out clean.
Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
Whisk powdered sugar and milk until smooth. Drizzle over cooled bread before serving.
