For the Filling:
1 ½ lb blackberries
3 medium to large cooking apples
For the Crumble:
12 oz self-raising flour
6 oz butter
6 oz caster sugar
For the Custard:
2 tbsp real custard powder (I use Bird's)
2 tbsp sugar
¾ pint semi-skimmed milk
Preheat the oven to 180 °C. Begin by peeling your apples and chopping them into thin segments of about 1" square, depending on how chunky you'd like your filling. Place these in a medium sized saucepan, along with the blackberries and about ½ a cup of water. Simmer this on a low heat for about 10 minutes, turning occasionally with a wooden spoon, until the fruit turns a lovely shade of red.
While this is simmering away, put the flour and the butter into a food processor and blast until it looks like breadcrumbs (usually about 20 seconds). Pour in the sugar and blast again just long enough to allow the sugar to mix in (about 2 seconds). It is important not to over-blend the mixture as it will begin to turn to pastry if you're not careful! (If you don't have a food processor, or just want to be au naturale, you can massage the flour and butter together with your fingers until it turns to a breadcrumb-esque texture, then gently fold in the sugar, ensuring the ingredients are evenly mixed together.)
Once your fruit resembles a palette of reds that make you want to take up painting, move them off the heat and strain into a 9" diameter oven proof dish. This should fill the dish to just below half way. Sprinkle some sugar over the fruit to stop it tasting too sharp. The amount is up to you, but I recommend using a level teaspoons worth. Next, pour your crumble mixture over the top and loosely spread out with your fingers.
Now place on the middle shelf of a preheated oven, at 180 °C for 30 minutes, or until the top of the crumble is just beginning to brown. Turn off the heat and leave to sit (I prefer to let it sit in the oven while preparing the custard, as it just browns off the edges a little bit more) until you are ready to eat it.
For the Custard: Heat the milk in a small pan on the hob, until it is almost at the boil. Mix your custard powder and sugar in a bowl, and add a little bit of the milk to make a paste. Bring the milk to the boil, then pour over the paste and stir constantly until it turns. It should have a nice thick consistency, but still be runny enough to pour from a jug.
Serve the crumble with a good helping of custard and warm your toes by the fire - you've earned it!