Pre-heat the oven to 180°C (350°F, Fan 160°C, Gas Mark 4)
Chop 300g of apple into small chunks around 2cm squared and toss it into a big bowl. Add the blackberries, 30g of plain flour, 30g of light soft brown sugar, and 2 grams of cinnamon, then mix together until the fruit is generally coated
Pour the contents into a sturdy oven dish
Swiftly blend 70g of walnuts so that they resemble breadcrumbs and maintain a crumbly texture
In a clean bowl, combine the walnuts, 100g of plain flour, 50g of light brown soft sugar and 50g of chilled,chopped butter. Then, using the tips of your fingers rub the mix together until it again resembles breadcrumbs
Pour the resulting topping over the fruit mix, and spread evenly
Bake in the middle of the oven for exactly 45 minutes
Eat on its own, or serve with traditional custard or a simple chocolate sauce