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.