Preheat oven to 350F. Grease and flour three 6" cake rounds and line with parchment.
In a medium bowl, whisk flour, baking powder, spices, and salt until well combined. Set aside.
Using a stand mixer fitted with a paddle attachment, cream butter and dark brown sugar on med-high until pale and fluffy (approx 3mins).
Reduce speed and add eggs one at a time fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture and applesauce, beginning and ending with flour (3 additions of flour and 2 of applesauce). Fully incorporating after each addition.
Bake for 30-35mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack. Allow to cool completely.
Preheat oven to 350F and line a baking sheet with parchment.
Combine all ingredients in a medium bowl until clumps form. Spread on parchment lined baking sheet and bake for 5-7mins.
Cool completely on baking sheet. Break up any larger chunks if needed.
Cinnamon Cream Cheese Frosting:
Beat butter and cream cheese until fluffy (2 mins). Add powdered sugar one cup at a time. Add vanilla & cinnamon and beat until fluffy (3 mins).
Place one layer of cake on a cake stand or serving plate. Top with 2/3 cup of frosting and 1/4 cup streusel (or more if desired). Repeat with remaining layers and apply a thin coat of frosting all over the cake. Chill for 20mins.
Use the remaining frosting to frost the cake with rustic swoops. Use extra streusel to decorate bottom and top of cake if desired.