Preheat the oven to 350ºF. Line a 9x5-inch loaf pan with parchment paper, then grease with cooking spray.

In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt.

In a large bowl, beat together the sugar and butter until light and fluffy, about 1 minute. Add in the eggs and vanilla. Mix until combined.

Mix in the flour mixture 1/2 at a time, alternating with buttermilk. Do not overmix. Set the batter aside.

For the crumble topping, in a medium-sized bowl, combine butter, light brown sugar, salt, and cinnamon. Add the flour. Using a fork, mix until the mixture is crumbly. Set aside.

In a separate bowl, coat the diced apples in cinnamon. Mix in 1/3 the apple mixture in the batter.

Pour 1/2 the batter into the prepared pan. Layer another 1/3 of the apples. Pour the remaining batter. Tap loaf pan onto the counter. Top the loaf with an even layer of the apple mixture and crumble topping.

Bake for 60-80 minutes or until a toothpick inserted in the center of the cake comes out mostly clean. If the top of the loaf gets too dark while baking, you can loosely cover it with foil.

Remove the loaf from the oven and allow to cool for 15 minutes in the pan. Transfer to a cooling rack to cool completely before glazing.

For the glaze, whisk the ingredients together until smooth. Drizzle over the cooled loaf.