Preheat oven to 375 degrees F (190 degrees C) and spray a 2-quart baking dish with nonstick cooking spray or grease with butter.
To make the crumble, whisk flour, salt, baking powder, cinnamon and sugars together in a large mixing bowl.
Using a cheese grater, grate in the frozen butter (you could cut the butter in with a pastry cutter, if you prefer). Gently toss the butter into the flour mixture until coated.
Using a fork, stir in vanilla and egg yolks until egg is mostly absorbed. Add vinegar and give the mixture another stir. Use your hands to finish incorporating all of the ingredients. Mixture should clump, but remain mostly dry. If your mixture is not clumping, add another teaspoon of apple cider vinegar. Set crumble aside.
To make the fruit filling, combine apple slices, blackberries, lemon zest, lemon juice, sugar, and cornstarch in a separate medium mixing bowl.
Transfer about 1/2 of the crumble mixture into the bottom of baking dish. Press mixture down using a flat measuring cup or damp hands. Pour the berry mixture over the crust. Add the remaining crumble mixture on top. Some small clumps are best!
Bake for 40 to 45 minutes and until top is golden brown and blackberry juice is bubbling. Allow the crumble to cool for about 20-30 minutes. Serve with a scoop of vanilla ice cream and enjoy!