Melt the butter in a saucepan.
Move the saucepan from the stove. Add salt and brown sugar to the melted butter. Add oat flour and whole wheat flour. Add milk and mix until well combined.
Transfer the dough to a greased cast iron pan or use a pie plate and press with your hand or spatula to flatten the dough.
Chill in the fridge for around 20 minutes.
Slice the apples. Add the apples to a bowl and sprinkle some lemon juice, add sugar and cinnamon and mix.
Preheat oven to 180°C (350° F).
Pour in apple sauce on the dough. Arrange the apples slices from the edges to the center.
Bake for 1 hour. Allow to cool completely before slicing. Enjoy!