Easy, fluffy chocolate party tray bake cake without eggs or dairy!
Preheat your oven to 180°C (or 160°C if you're using a fan oven). Line an 8x10-inch tin with baking paper.
Melt the margarine and stir in the coffee granules until dissolved. Leave to cool for a few minutes.
Mix the soy milk and vinegar together and set aside. This will act as your vegan buttermilk.
In a large bowl, mix together the flour, bicarbonate of soda, cocoa powder and caster sugar.
Add the melted margarine and the vegan buttermilk into the bowl. Mix well to make a smooth cake batter.
Pour the cake batter into your lined tin and spread it out evenly. Bake for 25-30 minutes, until a toothpick through the centre comes out clean.
Let the cake sit in the tin for around 10 minutes then carefully flip it out onto a wire rack. Peel the baking paper off the bottom and leave to cool completely.
In a large bowl, mix together the vegan butter and vanilla extract.
Slowly add the icing sugar and cocoa powder, mixing as you go, until smooth. Use as much of the plant-based milk as you need to help loosen it.
Once all of the icing sugar and cocoa powder has been mixed in, use a stand mixer or electric whisk to whisk it for a minute or so until light and fluffy.
Spread the buttercream over the cooled cake and top with chocolate buttons. When the icing is firm to the touch, cut into squares and enjoy.