Step 1. Preheat the Oven

Preheat your oven to 180°C (350°F) and grease a 9-inch baking dish lightly with butter.

Step 2. Prepare the Apple Filling

Peel, core, and slice the apples into thin wedges. Place the apple slices in a mixing bowl and toss with the caster sugar and ground cinnamon (if using) until well-coated. Transfer the apple mixture into the prepared baking dish, spreading it out evenly.

Step 3. Make the Crumble Topping

In a separate bowl, combine the flour, cold cubed butter, brown sugar, and a pinch of salt. Using a pastry cutter or your fingertips, rub the butter into the flour and sugar until the mixture resembles coarse breadcrumbs. If desired, stir in rolled oats or chopped nuts for extra texture.

Step 4. Assemble the Crumble

Sprinkle the crumble topping evenly over the apples, ensuring all the fruit is covered. Do not press down on the topping; it should be loose to create a crumbly texture.

Step 5. Bake the Crumble

Place the baking dish in the preheated oven and bake for 35-40 minutes, or until the topping is golden brown and the apple filling is bubbling around the edges.

Step 6. Serve and Enjoy

Allow the apple crumble to cool slightly before serving. Serve warm with a scoop of vanilla ice cream, a dollop of whipped cream, or a drizzle of custard for the perfect dessert.