Preheat the oven to 180C/160C Fan/Gas 4 and line 2 x 12-hole muffin tins with 18 paper cases.
Sift the flour, cocoa powder, baking powder and bicarbonate of soda into a large mixing bowl. Add the caster sugar and a pinch of salt.
Add the sunflower oil, eggs and milk and beat until smooth. Add the boiling water and mix again until silky smooth.
Scoop the batter into a large mixing jug and pour evenly between the paper cupcake cakes. Bake on the middle shelf of the preheated oven for 20–25 minutes, or until well-risen and a wooden skewer inserted into the middle of the cakes comes out clean.
Leave the cakes to cool in the tin for about 5 minutes, then transfer to a wire rack to cool completely.
Meanwhile, make the buttercream. Beat the butter, icing sugar and cocoa powder together using an electric hand whisk, until pale and fluffy. Pipe or spread the buttercream over the top of the cupcakes and scatter over the chocolate decorations. Store in an airtight container.
- For the cupcakes
- 175g/6oz plain flour
- 40g/1½oz cocoa powder
- 1½ tsp baking powder
- ½ tsp bicarbonate of soda
- 250g/9oz caster sugar
- pinch salt
- 100ml/3½fl oz sunflower oil
- 2 large free-range eggs
- 2 tbsp milk
- 125ml/4fl oz boiling water
- For the buttercream
- 200g/7oz unsalted butter, softened
- 130g/4½oz icing sugar
- 15g/½oz cocoa powder
- handful chocolate decorations