Put the pears and apples in a large saucepan with the sugar, cinnamon and apple juice. Cover and cook gently, stirring occasionally, for about 10 minutes or until the fruit is just tender. Transfer to an ovenproof dish.
Make the topping. Place the flour and butter in a food processor and whizz until the mixture resembles fine breadcrumbs. Alternatively, place the flour in a large bowl, add the butter and rub in with the fingertips until the mixture resembles fine breadcrumbs. Stir in the sugar and nuts, then sprinkle over the fruit and press down gently.
Place in a preheated oven, 200°C (400°F), Gas Mark 6, for 20–25 minutes until golden and bubbling. Serve with crème fraîche or cream.