Vegan Chocolate Sheet Cake

• 250 ml soy milk (1 cup)
• 2 Teaspoons apple cider vinegar
• 200 g self-raising flour (1+½ cups)
• ½ Teaspoon baking soda
• 2 Tablespoons cocoa powder
• 200 g caster sugar (1 cup)
• 95 ml vegetable oil (⅓ cup + 1 tablespoon)
• 1 Teaspoon vanilla extract
• 80 g vegan chocolate chunks ((½ cup) optional)

For the ganache:

• 200 g Vegan dark chocolate, finely chopped (7 oz)
• 80 ml soy milk (⅓ cup)

To top (optional):

• dark chocolate shavings
• Vegan white chocolate shavings