Preheat oven to 350 degrees F. Grease and flour a 9x5 inch loaf pan.
Mix brown sugar and cinnamon together in a bowl and set aside. Beat white sugar and butter together in a bowl using an electric mixer until smooth and creamy. Beat in eggs, 1 at a time, until incorporated; add vanilla extract.
Combine the flour and baking powder together in another bowl; stir into creamed butter mixture. Mix milk into batter until smooth.
Pour half the batter into prepared pan. Next add half the apples and half the brown sugar cinnamon mixture. Lightly pat apples into batter.
Pour the remaining batter over apple layer; top with remaining apples and add more brown sugar cinnamon mixture. Lightly pat apples into batter; swirl brown sugar mixture through apples using a finger or spoon.
Bake in preheated oven until a toothpick inserted in center of loaf comes out clean, 30-40 minutes. This recipe took 65 minutes in my oven.