Easy vegan chocolate cake

Name: Easy vegan chocolate cake
Prep time: 30 min
Cook time: 25 min
Total time: 55 min
Cuisine: British
Ingredients: a little dairy-free sunflower spread for greasing; 1 large ripe avocado (about 150g); 300g light muscovado sugar; 350g gluten-free plain flour; 50g good-quality cocoa powder; 1 tsp bicarbonate of soda; 2 tsp gluten-free baking powder; 400ml unsweetened soya milk; 150ml vegetable oil; 2 tsp vanilla extract; 85g ripe avocado flesh, mashed; 85g dairy-free sunflower spread; 200g dairy-free chocolate 70% cocoa, broken into chunks; 25g cocoa powder; 125ml unsweetened soya milk; 200g icing sugar sifted; 1 tsp vanilla extract; gluten-free and vegan sprinkles to decorate