Preheat oven to 350°F. Grease and flour a 9 x 5-inch non-stick loaf pan.

Mix brown sugar and cinnamon together in a bowl.

Beat white sugar and butter together in a bowl using an electric mixer until smooth and creamy. Beat in eggs, one at a time, until incorporated; add vanilla extract.

Combine flour and baking powder together in another bowl; stir into creamed butter mixture. Mix milk into batter until smooth.

Pour half the batter into the prepared loaf pan. Next add half the apples and half the brown sugar cinnamon mixture. Lightly pat apple mixture into batter.

Pour the remaining batter over apple layer; top with remaining apples and brown sugar/cinnamon mixture. Lightly pat apples into batter and swirl brown sugar mixture through apples using a finger.

Bake in the preheated oven until a toothpick inserted in the center of the loaf comes out clean, 45-55 minutes. Baking time may vary depending on the oven, so take a peek at 40 minutes and see how the cake looks like.