Cooking the Fruit Filling

Cup of Yum
1. Preheat oven to 180 °C (fan oven).
2. Peel, core, and slice the apples.
3. Place the apples in a pan and add sugar along with the cinnamon, give it a good stir to make sure all apples are evenly covered with cinnamon and sugar.
4. Cook until the apples are slightly softened, remove from the heat, and then add the blueberries.
5. Let the filling cool down and proceed with preparing the crumble mixture.

Prepare the Crumble Mixture

1. Cut the cold butter into small cubes and place it in a mixing bowl with the flour.
2. Rub them together with your fingertips until it looks like bread crumbs. 
3. Add the sugar and chopped walnuts to the crumb and lightly rub the mixture with your fingertips until combined, without overworking it.

Build the Crumble and Cook

1. Transfer the apple and blueberry filling into a baking dish 20cm x 30 cm (13" x 9").
2. Sprinkle the crumble over the filling and gently press using a silicon spatula.
3. Bake in the preheated oven for 25 to 30 minutes or until it looks golden brown.
4. Let it rest for 5-10 minutes before serving.