Preheat the oven to 350 degrees.

In a mixing bowl, cream together the ⅓ cup butter and ⅔ cup sugar until smooth.

Add the eggs, applesauce, and 2 tsp vanilla to the mixing bowl, and beat until combined.

Mix in the flour, baking powder, and cinnamon until well incorporated.

Pour the sour cream into the bowl and beat on high until the batter is smooth.

Heat a skillet over medium heat on the stove, and add the apples, ½ cup sugar, ½ tsp cinnamon, pinch of nutmeg, water, and cornstarch to it. Continue to cook until the apples are softened and the sauce has thickened.

Mix together the ½ cup brown sugar and ½ tsp cinnamon in a bowl and set aside.

Place half of the cake batter in an even layer on the bottom of a well-greased baking dish.

Cover the batter with the apple filling, and sprinkle ¾ of the brown sugar mixture on top of them.

Layer the last half of the cake batter on top of the apple filling, and top with the remaining brown sugar mixture.

Bake for 30-35 minutes, or until cooked through.

While the cake is baking, add the ingredients for the glaze to a mixing bowl, and beat until smooth and creamy.

Immediately pour the glaze evenly over the cake when it is removed from the oven. Let sit to allow the glaze to harden a bit before serving.