Preheat oven to 350 degrees F. Liberally grease a 9-10" springform pan with cooking spray and set aside.
First, make your crumb. In a large bowl, whisk together the brown sugar, flour, salt and cinnamon until blended. Pour in the melted butter and stir to combine until moist, large clumps form. Set aside.
Meanwhile for the cake, in the bowl of a stand mixer, cream together the butter and sugar for about 2 minutes or until light and fluffy. Add in the eggs, one at a time, then add in the vanilla and sour cream. Lastly, add in the flour, baking powder, baking soda, nutmeg and salt until a soft, thick batter forms.
Spread HALF of the batter into the prepared pan. Batter will be thick, so work with it to spread it out. It'll only be a thin layer. Top with the chopped apples and HALF of the crumb mixture. Top with the remaining cake batter and finish with the remaining crumb mixture.
Bake for approx. 50-60 minutes or until a toothpick inserted near the center comes out clean or with moist crumbs. Cool completely in the pan before glazing, then cut into slices.