Vegan Apple Crumble Bars

For the shortbread base:

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

For the apple filling:

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

For the crumb topping:

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