Vegan chocolate fudge cake

For the cake
225g plain or light spelt flour
1½ tsp bicarbonate of soda
1 good pinch salt
75g cocoa
250g dark muscovado sugar
75g coconut oil
1½ tsp vinegar (I use cider)
For the icing
75g coconut oil
50g dark muscovado sugar
1½ tbsp cocoa
150g dark chocolate (70% cacao), finely chopped
Heat the oven to 180C/350F/gas 4. Grease an 18cm round springform cake tin with oil and line the base with baking parchment.
Put all of the icing ingredients except the chopped chocolate into a heavy-based saucepan with 60ml cold water. Heat until the coconut oil is melted, making sure the mixture doesn’t boil, then turn off the heat, add the chocolate and leave it to sit. After about a minute, whisk until you have a dark glossy icing and set aside. It should be cool and thick by the time the cake has baked and cooled.
For the cake, whisk the flour, bicarbonate of soda, salt and cocoa together in a bowl. Make sure there are no lumps of bicarbonate of soda.
In a separate bowl, mix the sugar, 375ml of just-boiled water, the coconut oil and vinegar. When the coconut oil has melted, stir into the dry ingredients, then pour into the prepared tin.
Bake for 35-40 minutes. When it is ready, the cake should come away from the edges of the tin and a skewer inserted into the centre will come out clean. Cool for 30 minutes in the tin, then transfer to a wire rack to cool completely.