Preheat oven to 180°C. Combine the flour, sugar, butter and oats in a bowl.
Use your fingertips to rub the butter into the flour mixture until the mixture resembles fine breadcrumbs. Stir in the walnuts.
Spoon the apple into a 1.5L (6-cup) capacity ovenproof dish. Scatter the walnut mixture evenly over the apples. Bake in oven for 20-25 minutes or until golden. Spoon the apple crumble into serving bowls. Serve with ice-cream.
Thank you Taste: www.taste.com.au/recipes/17794/apple+crumble