For the cake: Preheat the oven to 350°F (175°C). Grease and flour an 8-inch round or square cake pan.
- In a large bowl, combine the flour, baking soda, baking powder, cinnamon, nutmeg, and salt. Stir to combine.
- In a separate bowl, whisk together the melted coconut oil, applesauce, maple syrup, vanilla extract, and almond milk.
- Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.
- Pour the batter into the prepared cake pan and spread it evenly.
- For the apple butter filling: In a small bowl, mix the apple butter with the chopped apples, maple syrup, and cinnamon. Spoon the apple butter mixture over the cake batter, spreading it evenly over the surface. It will sink slightly into the batter during baking.
- For the crumb topping: In a separate bowl, mix together the flour, oats, coconut sugar, cinnamon, and salt. Add the melted coconut oil and mix until the crumb topping comes together and resembles coarse crumbs.
- Sprinkle the crumb topping evenly over the apple butter filling.
- Baking: Bake the cake for 35-40 minutes, or until a toothpick inserted into the center comes out clean (except for a little bit of apple butter). The top should be golden and the cake should have risen.
- Allow the cake to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.