Preheat oven to 350℉
Grease a large baking dish with butter.
Combine the apples (600g) with the sugar (100g), cinnamon (1 tsp), and vanilla (1 tsp) in a large bowl and mix until the apples are evenly coated.
Pour apples into the prepared baking dish.
In a bowl combine the flour (60g), oats (30g), brown sugar (145g), salt (¼ tsp), and cinnamon (½ tsp). Mix well. Pour in the melted butter and mix with a fork or pastry cutter until crumbly.
Sprinkle the topping evenly over the apples.
Bake in the oven for 50-60 minutes until the apples are soft and the topping is browned.
Let cool a bit before serving. With vanilla ice cream would be best.