- Preheat oven to 350 degrees F. 
- Prepare a round, 9 inch cake can by spraying it liberally with coconut oil. 
- Add the flours, baking soda, sea salt, and cinnamon to a large mixing bowl, and mix together well. 
- In a small bowl, mix together yogurt, coconut oil, date syrup, and eggs. 
- Add wet ingredients to dry cake ingredients, and mix just until the dry ingredients are wet, without overmixing. Set aside. 
- Peel and slice apples, keeping them in a bowl of water with lemon juice to keep from browning. 
- In a small bowl, mix together the flours, brown sugar, and cinnamon for the crumb topping. Drizzle the coconut oil in, and mix until a crumb texture is reached. Set aside. 
- In the prepared cake pan, first layer the cake batter, then top with the sliced apples, pressing down slightly into the cake. 
- Top the cake and apples with the crumb topping. 
- Bake for 35-40 minutes, pressing down past the apples with a skewer or fork to check doneness in the center of the cake. 
- Top with caramel sauce when ready to serve.