Blueberry and Lime Coconut Sugar Cake

Name: Blueberry and Lime Coconut Sugar Cake
Cuisine: American
Ingredients: 40g (3 tbsp) butter (melted and slightly cooled); 100g (⅚ cup) spelt flour (see note 1); 2 tsp baking powder; ¼ tsp bicarbonate (baking soda); 50g (¼ cup) coconut sugar (see note 2); 1 egg (large); 75g (⅓ cup) Greek yoghurt (see note 3); 50ml (3 tbsp) milk (see note 4); 1 tips vegetable oil; juice of half a lime; ½ tsp vanilla extract; 100g (3½ oz) blueberries (see note 5); icing sugar (optional)