Preheat the oven to 180C/350F/gas mark 4 and line a muffin tray with two cupcake cases.
Place the flour, sugar, cocoa powder, bicarbonate of soda and salt in a bowl and whisk to combine. Add the milk, sunflower oil, vinegar and vanilla extract and whisk until smooth.
Divide the mixture between the two cases and bake for 18-20 minutes until a skewer inserted into the centre comes out clean.
Carefully transfer the cupcakes to a wire rack and set aside to cool.
Melt the chocolate in short bursts in the microwave, stirring every 10 seconds. Set aside to cool slightly.
Place the vegan spread or butter in a bowl and sift in the cocoa powder and icing sugar. Use a spatula to mix them together until smooth. Add the melted chocolate and stir well.
Place the buttercream in the fridge for 5 minutes to firm up a little then slather it on top of the cooled cupcakes, top with chocolate shavings and dig in.