Preheat oven to 350 degrees. Use a 9x5-inch loaf pan and spray with non-stick spray or line with foil and spray with non-stick spray to get out easily for slicing.
Mix 1/3 cup brown sugar and 1 teaspoon cinnamon together in a bowl. Set aside.
Combine & whisk 1 & 1/2 cups flour and 1 & 3/4 teaspoons baking powder together in another bowl and set aside.
In another medium-sized bowl, beat 2/3 cup granulated sugar and 1/2 cup softened butter together using an electric mixer until smooth and creamy.
Beat in 2 eggs, one at a time until blended in; add in 1 & 1/2 teaspoons vanilla extract and mix in.
Add the flour mixture into creamed butter mixture and mix until blended.
Mix 1/2 cup milk into batter and continue mixing until smooth.
Pour half the batter into the prepared loaf pan; add half the chopped apple mixture with the sugar and cinnamon added in.
Sprinkle 1/2 of the brown sugar/cinnamon mixture you set aside earlier, on top of apple layer.
Pour the remaining batter over apple layer and top with remaining chopped apples, then the remaining brown sugar/cinnamon mixture.
Lightly pat apples into batter; swirl brown sugar mixture through apples using knife or spoon.
Bake in the preheated oven until a toothpick inserted in the center of the loaf comes out clean, approximately 60 minutes.
To make glaze, mix 1/2 cup powdered sugar and 1 to 3 tablespoons milk or cream together until well mixed. (Place mixture in microwave for 10 seconds to get it pourable if it needs a boost.)
Let loaf rest in pan for about 15 minutes before removing from pan to let cool off completely on a cooling rack. Drizzle with glaze.
If you want more glaze, make a double batch. :)