Start by making the chocolate sauce; whisk together the cocoa powder, cornflour (cornstarch), sugar, espresso powder and salt in a saucepan then gradually whisk in the milk, making sure that there are no lumps.
Cook the mixture over a medium-low heat, stirring constantly, until it comes up to the boil and thickens. Allow to simmer for 1 minute then remove from the heat and add the chopped dark chocolate, vegan butter and vanilla extract, stir until melted and smooth then set aside.
To make the pancakes, whisk together the plain flour, cornflour (cornstarch), cocoa powder, baking powder, salt and sugar in a large bowl. Gradually whisk in the milk to make a smooth batter then whisk in the melted vegan butter, cider vinegar and vanilla extract.
Don't leave the batter sitting around before you cook it as the pancakes won't be as fluffy.
Place a good non-stick frying pan (or two for speed) over a low heat. If the pan is very non-stick then there is no need to grease it, otherwise you will need to add a little sunflower oil or vegan butter.
Pour about ¼ cup of the batter into the pan and cook for a couple of minutes until bubbles appear in the surface and the batter has set around the edges. Flip the pancake over and cook for another couple of minutes until cooked through. Repeat with the rest of the batter, you should get about twelve pancakes.
Re-warm the chocolate sauce if needed and serve the pancakes topped with the sauce and some fresh berries.