Preheat your oven to 350°F (175°C) and prepare a 9x5-inch loaf pan by greasing it or lining it with parchment paper.

In a medium bowl, combine diced apples with brown sugar and ground cinnamon, stirring until the apples are well-coated.

In a large mixing bowl, cream the softened unsalted butter with granulated sugar using an electric mixer on medium speed for about 3-4 minutes.

Beat in the eggs one at a time, followed by pure vanilla extract, ensuring everything is combined.

In another bowl, whisk together the all-purpose flour and baking powder. Gradually add this to the wet ingredients, alternating with milk.

Pour half of the batter into the prepared loaf pan, then spoon half of the cinnamon apple mixture on top. Add the remaining batter and top with the rest of the apples.

Bake for 50-60 minutes, checking doneness with a toothpick at 45 minutes. The bread should be golden brown and spring back when touched.

Once baked, cool in the pan for about 10 minutes before transferring to a wire rack. For the glaze, whisk together powdered sugar, milk, and vanilla until smooth.