Mix the Cinnamon Sugar: Combine brown sugar and cinnamon in a small bowl and set aside.

Prepare the Apple: Peel and chop the apple into small pieces, then place in a bowl and set aside.

Cream Butter and Sugar: In a large bowl, beat softened butter and granulated sugar using a hand or stand mixer on medium speed until grainy and well blended.

Add Eggs and Vanilla: Mix in the eggs and vanilla extract until smooth. The batter should be slightly soupy with no visible lumps.

Add Dry Ingredients: Add flour, baking powder, and salt to the wet mixture. Stir gently until combined.

Incorporate Milk: Pour in the milk and stir with a spoon until a smooth batter forms. Avoid overmixing.

Layer the Batter: Pour half of the batter into a greased loaf pan. Add half the chopped apples and sprinkle with half of the brown sugar mixture. Repeat the layering with the remaining ingredients.

Bake to Perfection: Place the loaf pan in the center rack of a preheated oven at 350°F (175°C) and bake for 50–55 minutes, or until a toothpick inserted in the center comes out clean.

Cool and Serve: Let the bread rest in the pan for 10 minutes before transferring it to a cooling rack. Slice and enjoy warm with butter or on its own.