Bring a pan of water to boil over the stove and then set to simmer. Break the chocolate into smallish pieces. Put a glass bowl on top of the pan and put chocolate in the bowl until fully melted. Once melted, turn pan off and separate 1/3 of the chocolate to another large bowl.
Preheat the oven to 180 C / Gas 4.
In the bowl with 2/3 of chocolate, add 170g of vegan butter and 350g sugar and mix until smooth. Then add baking powder, salt, vanilla extract and the oil. Mix. Then sieve the flour gradually between mixes until all the flour has been mixed. If your cake mix looks a little dry or stodgy add small amounts of soya milk until smooth and thick cream-like.
Get a large cake tin and grease with butter or cover with greaseproof paper.
Bake cake in oven until it looks like the top of a tray of brownies, about 30 minutes. Don't let it dry out.
While your cake is in the oven, you can make your icing. Take the bowl with the rest of the chocolate in it and add 100g of vegan spread, mix until smooth. Then sieve the icing sugar gradually between mixes until all mixed in. If it looks dry or stodgy add small amounts of soya milk until desired consistency. Make sure your cake is coolish before adding the icing.
Serve warm. If you re-heat a piece in the microwave for 30 seconds, it still stays moist up to 4 days after making :)
If you want to make it a little different, add a little extra flavor to the icing. Peppermint is my favorite, and orange, vanilla, cherry, cinnamon or caramel are nice, too.