Preheat the oven to 350° F.

Grease an 8-inch round cake pan, or springform pan.  I used coconut oil.

Make the cinnamon crumb topping by whisking together flour, brown sugar, coconut sugar, cinnamon, and nutmeg.  Pour the melted butter and stir with a fork until the mixture is thoroughly incorporated.   Refrigerate the crumb topping while you prepare the cake batter.

In a large mixing bowl, cream the butter and sugar until light and fluffy, add the egg and beat for 1 minute.  Add vanilla, applesauce, and sour cream and beat until incorporated.

In a medium bowl, whisk together the flour, cinnamon, baking powder, baking soda, and salt.   Add the dry ingredients to the wet ingredients and beat just until combined.

Add the peeled and chopped apples to the batter and stir to combine.

Pour half the batter into the prepared baking pan, then top with half the streusel topping.  Pour the remaining batter, then the remaining streusel crumb topping, gently spreading with an offset spatula if necessary.

Bake for 35 minutes.  Check if the cake is done by inserting a knife or toothpick into the center of the cake.  if it comes out clean, the cake is done.

Let the cake cool slightly before topping with the maple glaze.

For the glaze - in a small bowl, combine the powdered sugar, maple extract, vanilla extract, and milk and stir with a spoon.  Use a spoon to drizzle the glaze on the cooled cake.