Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan or line it with parchment paper for easy removal.
Prepare the Dry Ingredients: In a large mixing bowl, combine the flour, sugar, baking powder, cinnamon, and salt. Mix well to combine.
Prepare the Wet Ingredients: In a separate bowl, whisk together the eggs, milk, and melted butter until smooth.
Combine Wet and Dry Ingredients: Gradually add the wet mixture to the dry ingredients, stirring just until combined. The batter will be thick.
Fold in the Apples: Gently fold the diced apples into the batter until evenly distributed.
Layer the Cinnamon Sugar: In a small bowl, combine the sugar and cinnamon for the cinnamon sugar layer. Spoon half of the batter into the prepared pan, sprinkle half of the cinnamon sugar mixture on top. Add the remaining batter and top with the rest of the cinnamon sugar. Use a knife to swirl the batter gently for a marbled effect.
Bake the Bread: Bake for 50-60 minutes, or until a toothpick inserted into the center of the bread comes out clean. If the bread starts to brown too quickly, cover it loosely with aluminum foil.
Cool and Glaze: Allow the bread to cool in the pan for 10-15 minutes before transferring it to a wire rack. In a small bowl, whisk together powdered sugar, vanilla extract, and milk to make the glaze. Drizzle the glaze over the cooled bread.
Serve: Slice the bread and serve once the glaze has set. Enjoy!