Vegan Apple Crumble Bars

For the shortbread base:

• 250 g plain flour (~2 cups)
• 80 g caster sugar (⅜ cups)
• 180 g vegan margarine ¾ cup, cold

For the apple filling:

• 330 ml water 1 + ⅓ cups, cold
• 2 Tablespoons cornflour (corn starch)
• 100 g caster sugar (½ cup)
• 1 Teaspoon cinnamon
• 4 green apple around ¼-inch thick, medium, peeled, cored and sliced

For the crumb topping:

• 300 g plain flour (~2+⅓ cups)
• 175 g brown sugar ¾ cup + 2 tablespoons, soft, light
• 200 g vegan margarine ¾ cup + 1 tablespoon, cold