Vegan Coffee Cake

For the sponge:

• 280 ml soy milk (1 cup + 2 tablespoons)
• 2 Teaspoons apple cider vinegar (or white vinegar)
• 1 Tablespoon instant coffee
• 250 g self-raising flour (~2 cups)
• ½ Teaspoon baking soda (bicarbonate of soda)
• 200 g caster sugar (1 cup)
• 100 ml vegetable oil (7 tablespoons)
• 1 Teaspoon vanilla extract

For the dairy-free coffee buttercream:

• 1 Teaspoon instant coffee
• 120 g Dairy-free margarine (½ cup)
• 300 g icing sugar (2 + ½ cups)