• Preheat the oven to 350°F(177°C). Grease 8 inch (20cm) square oven-proof dish and line the bottom and sides with parchment paper, about 2 inches(5 cm) of overhang on each side.

Apple Filling

• Place the chopped apples in a medium bowl.  Add the nutmeg, cinnamon, sugar and flour. Stir with a spoon or spatula until combined well.

Crust and Crumbles

• Put the rolled oats, flour, sugar and cinnamon in a medium bowl and stir with a spoon or a spatula.  Add the melted butter and stir.
• Set aside ⅓ of the mixture (to be precise it is 180 grams or almost loosely 1 cup) to use for the crumbles. Place ⅔ of the mixture into the dish. You can use your hand or a spoon to press the mixture to the dish. Put the apple mixture over the dough.** Sprinkle the dough that you set aside over the apples. You should gently press the crumbles so they stick to the apples and you can cut proper slices once cooled.
• Bake for almost 50 minutes or until the crumbles are golden brown.

Caramel Sauce

• While it is baking, make the caramel sauce. It is important that you add the heavy cream gradually and whisk it at the same time to avoid any lumps. You can find all the detailed information in those posts. If you already have your caramel sauce and want to use it, sure you can. You should remove it from the fridge so it will be in a pourable consistency. You can hasten this step by putting it in a pan over low-medium heat and stirring until you reach a pourable consistency. 

Assemble

• Let the dish cool at room temperature for 1 hour before pouring ½ of the caramel sauce on top.  Gently swirl the dish,  so the caramel sauce spreads.  You should wait at least half an hour before placing it in the fridge and you should let it completely cool for an extra 1 and ½ hours in the fridge as well.  This step is essential if you want to cut proper slices.
• Cut into 16 slices. If you prefer, you can add the extra caramel on top.