Step 1
Sift flour into a large bowl. Rub in butter with your fingers until mixture resembles fine crumbs. Stir in sugar vanilla cold water and baking powder until a firm dough forms.
Step 2
Knead dough gently and briefly on a floured work surface. Wrap in plastic wrap and let chill about 30 minutes.
Step 3
Place apples in a pot and cover with water. Bring to a boil; reduce heat and simmer gently until soft 15 to 20 minutes. Drain. Mash with a hand blender or potato masher into a thick puree; let cool.
Step 4
Preheat oven to 400 degrees F (200 degrees C). Grease a 9-inch pie plate.
Step 5
Press 2/3 of the dough into the pie plate evenly with your fingers to make the crust. Prick crust all over with a fork.
Step 6
Bake crust in the preheated oven until golden about 20 minutes.
Step 7
Grate remaining 1/3 of the dough onto a baking sheet to make crumbles.
Step 8
Bake crumbles in the preheated oven until golden about 10 minutes. Reduce oven temperature to 200 degrees F (95 degrees C).
Step 9
Place aquafaba and cream of tartar in the bowl of a stand mixer fitted with a whisk attachment. Beat on high gradually adding confectioners' sugar until meringue is stiff and glossy 10 to 15 minutes.
Step 9
Measure out 1 1/4 cup apple puree into a bowl. Stir in cinnamon. Spread apple-cinnamon puree over cooled pie crust. Spread meringue over the puree.