Set the oven to 350 degrees.

In a large mixing bowl, combine softened butter, applesauce, eggs, sugar, and vanilla extract. Mix until smooth.

Add almond flour, oat flour, baking powder, and salt. Combine until smooth.

In a separate bowl, mix melted butter, oat flour, white sugar, and cinnamon evenly.

For the crumble topping, combine brown sugar, almond flour, oat flour, and cinnamon with room temperature butter using your hands or a fork until crumbles form. Set aside.

Grease or line an 8×8 baking dish. Pour half of the cake batter into the dish and spread it evenly.

Add half of the cinnamon sugar filling on top and swirl it into the batter.

Spread the remaining half of the cake batter evenly on top. Add the rest of the cinnamon sugar filling and swirl it in.

Bake for 25 minutes. After baking, gently place the crumble topping on top and press it into the cake, especially in the middle where it might still be underbaked.

Bake for another 18 minutes.

Remove from the oven, let it cool completely, and then cut into squares. Enjoy!