Preheat oven to 350F.Use TWO (one for baking, one for layering) 9x5-inch loaf pans. Spray one with baking spray and leave one alone.Mix brown sugar and cinnamon together in a bowl. Set aside.Using a stand mixer with a paddle attachment cream together the butter and sugar until light and fluffy, about 3 mintues.Add the eggs, one at a time, scraping down after each addition.Add the vanilla and beat for 30 seconds.Add flour, salt, and baking powder together in another bowl and add into creamed butter mixture and stir until blended.Mix milk into batter and beat until smooth.Pour half the batter into the non-baking spray loaf pan; add half the apples, then half the brown sugar/cinnamon mixture, then drizzle ¼ cup salted caramel sauce.Pour the remaining batter over apple layer and top with remaining apples, then the remaining brown sugar/cinnamon mixture and remaining salted caramel sauce.Using and ice cream scoop (or large spoon), scoop the batter into the prepared loaf pan. This helps with getting the yummy caramel and brown sugar throughout the bread and I find it works much better than just swirling with a knife.Bake in the preheated oven until a toothpick inserted in the center of the loaf comes out clean, approximately 50-60 minutes.Let rest 5 minutes, flip out, and set on a wire rack to cool. Place that rack on a baking sheet for glazing. Let cool on rack for 15 minutes, then glaze.For the glaze:Whisk together the powdered sugar, salted caramel sauce, and milk together until smooth and there are no visible powdered sugar lumps.Drizzle glaze on cake.