Preheat your oven to 350°F. Grease and flour an 8 x 5-inch loaf pan or line it with parchment paper, and set it aside.

In a small bowl, whisk together the brown sugar and cinnamon. Set this fragrant mixture aside.

In a large mixing bowl, whisk together the eggs and granulated sugar until well combined.

Stir in the melted butter and vanilla extract until the mixture is smooth and cohesive.

Add all-purpose flour, baking powder, baking soda, and salt. Mix until just combined; the batter will be thick.

Gently fold in the chopped apples, ensuring they're well distributed.

Pour half of the batter into the prepared loaf pan. Sprinkle three-quarters of the brown sugar mixture over this layer.

Carefully spread the remaining batter on top, sprinkle the rest of the cinnamon sugar over it, and create a marbled effect using a knife.

Bake for 35 to 45 minutes, until golden and a toothpick comes out clean or with a few moist crumbs.

If browning too quickly, tent with foil for the last 10 to 15 minutes.

Let the apple bread cool completely before slicing and serving.