Prepare the apples: In a small bowl, toss the diced apples with the 1 ½ tsp cinnamon and brown sugar. Set aside.
Preheat oven: Preheat your oven to 350°F (175°C) and grease a 9x5-inch loaf pan.
Make the batter: In a large bowl, whisk together the flour, sugar, baking powder, and cinnamon. In a separate bowl, whisk the melted butter, eggs, vanilla, and milk. Add the wet ingredients to the dry ingredients and mix until just combined.
Layer the bread: Pour half of the batter into the prepared loaf pan. Spread half of the apple mixture on top of the batter. Repeat with the remaining batter and apples.
Bake: Bake for 50-60 minutes or until a toothpick inserted into the center comes out clean.
Cool: Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
Optional glaze: In a small bowl, whisk together powdered sugar, milk, and vanilla. Drizzle over the cooled bread for an extra sweet finish.