Preheat oven to 350°F. Grease and flour a 9 x 5 inch loaf pan or line with parchment paper. In a small bowl combine the brown sugar and cinnamon. Set aside.
½ cup brown sugar, 1 ½ teaspoons cinnamon
In the bowl of a stand mixer or using an electric mixer, beat butter until smooth, then add granualted sugar and continue to blend until fully incorporated.
½ cup unsalted butter, ⅔ cup granulated sugar
Add eggs and vanilla and blend until well combined.
2 large eggs, 2 teaspoons vanilla extract
Slowly add flour, baking powder, salt and then milk. Blend just until all ingredients are well combined. Do not over-mix.
1 ½ cups all purpose flour, 1 ½ teaspoons baking powder, ½ teaspoon fine sea salt, ½ cup milk
Pour HALF of the batter into the prepared pan.
Top batter with half of the diced apples, and half of the cinnamon sugar mixture.
1 large apple
Press apples and cinnamon sugar into the batter just a bit (with the back of a large spoon).
Pour the remaining batter on top of the apple layer (spread as needed), then top with remaining apples and remaining cinnamon sugar.
Again, press the apples and cinnamon sugar into the batter a bit.
Bake for 50-55 minutes, or until a toothpick inserted in the center of the loaf comes out clean.
Cool in the pan for 15 minutes, then transfer loaf to a cooling rack to continue cooling.