Sift the flour into a bowl, add the vegan butter and rub in with your fingertips until the mixture resembles fine breadcrumbs. Stir in other ingredients and mix to a firm dough. Knead the dough briefly and gently on a floured surface. Wrap in cling film and chill in the fridge for about 30 minutes.
Preheat the oven to 180 C / Gas 4. Grease a 23cm cake tin.
Take your dough from the fridge. Take 2/3 of your dough and spread it evenly with your fingers in the prepared tin. Prick the base all over with a fork, as this will release any trapped air, which is what causes the centre to rise up. Take another tin and grate the remaining dough to make crumbles.
Bake the base and crumbles in the preheated oven. After 10 minutes take your crumbles out and keep on the side. Keep your base in the oven for 10 more minutes. Take your base out and cool down your oven to 100 degrees C.
For the foam:
Meanwhile pour chickpea water to a bowl and start beating. Stir in a 1/2 teaspoon of cream of tartar and start adding icing sugar slowly. Beat till you have stiff peaks (usually takes about 10 to 15 minutes).
Take your base and pour the apple puree mixed with cinnamon. Spread the chickpea mixture on the top of your cake.
Bake for about 1 to 1/2 hours. Turn off the oven but leave your cake inside to cool down for about 45 minutes to 1 hour. After remaining time take your cake out and put your crumbles on the top. Enjoy!
Make sure that your aquafaba mixture (meringue mixture) is good enough – if your peaks are stiff the foam layer in your cake will be visible :) Make sure that you keep your cake in the oven till it cools down. Otherwise your aquafaba mixture will disappear if you sprinkle your crumbles straight after baking.