Place your apple chunks into the medium saucepan gently. Add the caster sugar and a tiny splash of water. Cook on medium heat for five minutes to soften them.

Spoon the softened apples into your clean baking dish. Sprinkle the ground cinnamon over the fruit layer evenly. Spread the mixture out so it looks flat.

Place your all-purpose flour into the large mixing bowl. Add the cold cubed unsalted butter into the flour. Rub them together using your clean fingertips gently.

Stop rubbing when the mixture looks like fine breadcrumbs. Stir in your crunchy demerara sugar with a spoon. This step ensures a wonderfully crispy texture.

Sprinkle the sweet crumble mix over your apples evenly. Do not press the topping down into the fruit. Keep it loose so it stays light and crunchy.

Place the dish inside your hot oven right away. Bake for thirty minutes until the top turns golden. The fruit sauce should bubble up around the edges.