Freezer Scavenge Berry Crumble

Being an Englishman, I have to have an awful lot of crumble recipes under my belt, and everyone has a little tip to make them better. This particular variation uses those immensely sour frozen mixed berries, and a very light, crunchy topping made even better with my newly-devised scientific strategy- quite often, crumble topping can be very sandy and claggy, and there are lots of ways to counter this, one being to make the topping by hand, not in a processor, and my new method is to add a tsp baking powder, and making the topping a bit clumpier with a splash of vinegar in water. The reaction of baking powder and vinegar makes it lighter, cruncher, crumblier, and somehow melts in your mouth to give a creamy texture. I make a crumble topping when I have a free moment to spare, say in the morning, and stash them in the freezer to make a crumble in a hurry. The fruits beneath are one of my favourites, given my porchant for tangy berries, and they give a lovely pool of glossy fruit juice that mixes divinely with custard. For a regular, everyday crumble, I recommend this over my chocolate pear version, but that one is still delicious, but I will have to apply this scientific topping to it.
1)Mix 150g plain flour, a pinch of salt and a tsp baking powder in a bowl, and cube in 75g soft unsalted butter; people say it should be ice cold, but it's an easier job and makes a more shortbread like crumble to have it soft. Rub it in, by lightly pressing the butter between the pads of your fingers, fluttering your fingers in a camp fashion as you do so. Stir in a handful of porridge oats, and a handful of demerara sugar, then quickly stir in a small tsp of water and white vinegar, giving it a gentle mix until you get a crumbly, dry dough.
2)Fill a pudding dish almost to the top with frozen berries, and stir in about 50g ground almonds and lots of vanilla sugar, as these berries are tart. Top with the crumble and bake at 180 degrees for 30 minutes, until very golden brown.